po: set gettext domain in Makevars so we don't have to patch the generated Makefile.in.in

https://bugzilla.gnome.org/show_bug.cgi?id=705455
Automatic update of common submodule

From dbedaa0 to d48bed3
adpcmenc: Properly set output format

Otherwise this will just error out if we only set caps on the srcpad.