Gio::ActionMap: Fix the ref count in lookup_action_vfunc()
Gio::ActionMap: Fix the ref count in lookup_action_vfunc()

* gio/src/actionmap.hg: Add refreturn in _WRAP_VFUNC(lookup_action).
Bug #758813.

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm