branching GLib-2.15 and Gtk+-2.13

[Tim Janik <timj imendio com>]

hey All.

there have been some pings recently on API changing bugs in
bugzilla, and i've heared about other API related bugs coming
up soon. so i guess next week would be a good time to branch Gtk+ for 2.13
and GLib for 2.15. at least, i intend to do it then if no one
beats me at it. ;)

feedback welcome.

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ciaoTJ