If 2.12.1 is started by a newly created user, all extensions are disabled.

The same happens when upgrading from 2.12.0 to 2.12.1 if the user has never changed the extension settings. 

How to reproduce:
- clear all gthumb settings:
gconftool-2 --recursive-unset /apps/gthumb
- install/update to gthumb-2.12.1
- start gthumb
- check, whether the extensions are enabled

Current behavior:
- all extensions are disabled

Expected behavior:
- the default extensions should be enabled (gth-main.c:1215)
or
- when upgrading from 2.12.0 to 2.12.1: all extensions should be in the same state as they were before the update)

Comments:
- the issue is caused by commit: http://git.gnome.org/browse/gthumb/commit/?id=bed6cab99568b0fea7e6db4f11dc716c0640ff00

- the patch has the following problem:
* if /apps/gthumb/general/active_extensions was never set before, gconf will automatically return the default from the schemas file
* check the default value:
gconftool-2 --recursive-unset /apps/gthumb
gconftool-2 -g "/apps/gthumb/general/active_extensions"
[]
* this means, that the gconf library will not generate an error and so the "default_extensions" in gthumb/gth-main.c:1269 are never used