This is an example of how the config files should work.
I have created a "gsocdummy" port, Portfile is in branches/gsoc10-configfiles/tools, I'm also using a gsoctestcase script that basically reset status of the branched installation, prefix /opt/mp-gsoc, to gsocdummy @0.1_0 as active port. This gsoctestcase script also upgrade Portfile to revision 1.

Here comes the shell:


Last login: Mon Aug 16 20:52:44 on ttys001
bimac:~ andrea$ mpswitch 
bimac:~ andrea$ echo $PATH
/Developer/Tools:/opt/mp-gsoc/bin:/opt/mp-gsoc/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/opt/X11/bin:/usr/X11/bin
bimac:~ andrea$ port installed gsocdummy
None of the specified ports are installed.
bimac:~ andrea$ gsoctestcase.sh 
--->  Cleaning gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Installing gsocdummy @0.1_0
--->  Activating gsocdummy @0.1_0
--->  Cleaning gsocdummy
Switching gsocdummy from revision 0 to 1
Ready to upgrade gsocdummy to @0.1_1
bimac:~ andrea$ port installed gsocdummy
The following ports are currently installed:
  gsocdummy @0.1_0 (active)
bimac:~ andrea$ port info --revision gsocdummy
revision: 1
bimac:~ andrea$ port cd etc
bimac:etc andrea$ ls
dummyrc  macports
bimac:etc andrea$ port provides /opt/mp-gsoc/etc/dummyrc
/opt/mp-gsoc/etc/dummyrc is provided by: gsocdummy
bimac:etc andrea$ GetFileInfo dummyrc 
file: "/opt/mp-gsoc/etc/dummyrc"
type: "\0\0\0\0"
creator: "\0\0\0\0"
attributes: avbstclinmedz
created: 08/16/2010 20:55:45
modified: 08/16/2010 20:55:45
bimac:etc andrea$ sudo port upgrade gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Computing dependencies for gsocdummy
--->  Installing gsocdummy @0.1_1
--->  Deactivating gsocdummy @0.1_0
--->  Cleaning gsocdummy
--->  Activating gsocdummy @0.1_1
--->  Cleaning gsocdummy
bimac:etc andrea$ GetFileInfo dummyrc 
file: "/opt/mp-gsoc/etc/dummyrc"
type: "\0\0\0\0"
creator: "\0\0\0\0"
attributes: avbstclinmedz
created: 08/16/2010 20:57:21
modified: 08/16/2010 20:57:21
bimac:etc andrea$ gsoctestcase.sh 
--->  Cleaning gsocdummy
--->  Uninstalling gsocdummy @0.1_0
--->  Cleaning gsocdummy
--->  Deactivating gsocdummy @0.1_1
--->  Cleaning gsocdummy
--->  Uninstalling gsocdummy @0.1_1
--->  Cleaning gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Installing gsocdummy @0.1_0
--->  Activating gsocdummy @0.1_0
--->  Cleaning gsocdummy
Switching gsocdummy from revision 0 to 1
Ready to upgrade gsocdummy to @0.1_1
bimac:etc andrea$ ls -l
total 8
-rwxr-xr-x   1 root  admin   20 16 Ago 20:57 dummyrc
drwxr-xr-x  10 root  admin  340 16 Ago 20:34 macports
bimac:etc andrea$ GetFileInfo dummyrc 
file: "/opt/mp-gsoc/etc/dummyrc"
type: "\0\0\0\0"
creator: "\0\0\0\0"
attributes: avbstclinmedz
created: 08/16/2010 20:57:32
modified: 08/16/2010 20:57:32
bimac:etc andrea$ sudo vi dummyrc 
bimac:etc andrea$ cat dummyrc 
Foo bar baz
text {dummy config}
bimac:etc andrea$ sudo port upgrade gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Computing dependencies for gsocdummy
--->  Installing gsocdummy @0.1_1
Error: Target org.macports.activate returned: Image error: run     port uninstall gsocdummy @0.1_1; port upgrade --config-upgrade gsocdummy
Log for gsocdummy is at: /opt/mp-gsoc/var/macports/logs/_opt_local_var_macports_sources_local_devel_gsocdummy/main.log
bimac:etc andrea$ sudo port uninstall gsocdummy @0.1_1;
--->  Uninstalling gsocdummy @0.1_1
--->  Cleaning gsocdummy
bimac:etc andrea$ sudo port upgrade --config-upgrade gsocdummy
--->  Computing dependencies for gsocdummy
--->  Computing dependencies for gsocdummy
--->  Installing gsocdummy @0.1_1
--->  File /opt/mp-gsoc/etc/dummyrc has changed
--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
current

--- /opt/mp-gsoc/var/macports/software/gsocdummy/0.1_0/opt/mp-gsoc/etc/dummyrc	2010-08-16 20:57:32.000000000 +0200
+++ /opt/mp-gsoc/etc/dummyrc	2010-08-16 20:57:48.000000000 +0200
@@ -1 +1,2 @@
+Foo bar baz
 text {dummy config}

--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
upgraded

--- /opt/mp-gsoc/etc/dummyrc	2010-08-16 20:57:48.000000000 +0200
+++ /opt/mp-gsoc/var/macports/software/gsocdummy/0.1_1/opt/mp-gsoc/etc/dummyrc	2010-08-16 20:58:00.000000000 +0200
@@ -1,2 +1 @@
-Foo bar baz
 text {dummy config}

--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
new
--->  Deactivating gsocdummy @0.1_0
--->  Cleaning gsocdummy
--->  Activating gsocdummy @0.1_1
--->  Cleaning gsocdummy
bimac:etc andrea$ GetFileInfo dummyrc 
file: "/opt/mp-gsoc/etc/dummyrc"
type: "\0\0\0\0"
creator: "\0\0\0\0"
attributes: avbstclinmedz
created: 08/16/2010 20:58:00
modified: 08/16/2010 20:58:00
bimac:etc andrea$ cat dummyrc 
text {dummy config}
bimac:etc andrea$ sudo rm dummyrc 
bimac:etc andrea$ gsoctestcase.sh 
--->  Cleaning gsocdummy
--->  Uninstalling gsocdummy @0.1_0
--->  Cleaning gsocdummy
--->  Deactivating gsocdummy @0.1_1
--->  Cleaning gsocdummy
--->  Uninstalling gsocdummy @0.1_1
--->  Cleaning gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Installing gsocdummy @0.1_0
--->  Activating gsocdummy @0.1_0
--->  Cleaning gsocdummy
Switching gsocdummy from revision 0 to 1
Ready to upgrade gsocdummy to @0.1_1
bimac:etc andrea$ sudo vi dummyrc 
bimac:etc andrea$ cat dummyrc 
Foo bar baz
this time changes should stay
text {dummy config}
bimac:etc andrea$ sudo port upgrade -u --config-upgrade gsocdummy
--->  Computing dependencies for gsocdummy
--->  Fetching gsocdummy
--->  Verifying checksum(s) for gsocdummy
--->  Extracting gsocdummy
--->  Configuring gsocdummy
--->  Building gsocdummy
--->  Staging gsocdummy into destroot
--->  Computing dependencies for gsocdummy
--->  Installing gsocdummy @0.1_1
--->  File /opt/mp-gsoc/etc/dummyrc has changed
--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
current

--- /opt/mp-gsoc/var/macports/software/gsocdummy/0.1_0/opt/mp-gsoc/etc/dummyrc	2010-08-16 20:58:52.000000000 +0200
+++ /opt/mp-gsoc/etc/dummyrc	2010-08-16 20:59:09.000000000 +0200
@@ -1 +1,3 @@
+Foo bar baz
+this time changes should stay
 text {dummy config}

--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
upgraded

--- /opt/mp-gsoc/etc/dummyrc	2010-08-16 20:59:09.000000000 +0200
+++ /opt/mp-gsoc/var/macports/software/gsocdummy/0.1_1/opt/mp-gsoc/etc/dummyrc	2010-08-16 20:59:25.000000000 +0200
@@ -1,3 +1 @@
-Foo bar baz
-this time changes should stay
 text {dummy config}

--->  Please choose one of:
---> 	(keep) current, install (new), show diff original-(current), show diff current-(upgraded):
keep
--->  Deactivating gsocdummy @0.1_0
--->  Cleaning gsocdummy
--->  Activating gsocdummy @0.1_1
--->  Cleaning gsocdummy
--->  Uninstalling gsocdummy @0.1_0
--->  Cleaning gsocdummy
bimac:etc andrea$ cat dummyrc 
Foo bar baz
this time changes should stay
text {dummy config}
bimac:etc andrea$ #enjoy
bimac:etc andrea$