docs: fix having a repeated id
docs: Improve documentation for AtkPlug and AtkSocket

https://bugzilla.gnome.org/show_bug.cgi?id=700800
docs: Extra note on AtkSocket documentation
docs: Fixed mention to atkobject methods
Release 2.9.2
docs: Fix documentation for atk_object_get_attributes()

Replace the wrong (transfer-none) annotation with (transfer-full), and
suggest to free it with atk_attribute_set_free() when done.

https://bugzilla.gnome.org/show_bug.cgi?id=701503
Merge branch 'master' of git://git.gnome.org/atk
JOHNE - Bump the master version number to 2.9.2