gobject: add autoptr support for GClosure
gobject: add autoptr support for GClosure

This commit defines a g_autoptr() cleanup function for use with
GClosure.

https://bugzilla.gnome.org/show_bug.cgi?id=786360

endlessm/glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib