libgdm: move out of gui/ directory

libgdm isn't a UI, so it's weird to be in a directory
called GUI.

This commit moves it up a layer.
daemon: get rid of greeter language selection

These days the greeter doesn't let you pick a language at log in time.

This commit drops the interface, since it's unused, and we don't have
any API guarantees in libgdm.
session: pass all language vars through to worker

Right now we set LANG based on the value of setlocale(),
and disregard all other language environment variables.

This commit just passes the environment variables through
wholesale.

http://bugzilla.gnome.org/show_bug.cgi?id=709105
session: add missing underscore

"set up" is two words when used as a verb, so the function
name "setup_session_environment" is missing an underscore.

This commit adds that underscore.
slave: fix infinite loop on shutdown

we stop something that calls stop in some circumstances.

This commit breaks the loop.

https://bugzilla.gnome.org/show_bug.cgi?id=712767
NEWS: update for release
configure: bump for release