Add test case for Gtk.ListStore custom sort
Add test case for Gtk.ListStore custom sort

This works in Python 2, but crashes in Python 3, another case of the segfaults
we get when C calls a Python callback in Python 3.

https://bugzilla.gnome.org/show_bug.cgi?id=674475

jdahlin/pygobject,GNOME/pygobject,davibe/pygobject,choeger/pygobject-cmake,thiblahute/pygobject,choeger/pygobject-cmake,MathieuDuponchelle/pygobject,choeger/pygobject-cmake,davidmalcolm/pygobject,davidmalcolm/pygobject,davidmalcolm/pygobject,jdahlin/pygobject,pexip/pygobject,sfeltman/pygobject,davibe/pygobject,GNOME/pygobject,sfeltman/pygobject,thiblahute/pygobject,sfeltman/pygobject,MathieuDuponchelle/pygobject,davibe/pygobject,thiblahute/pygobject,pexip/pygobject,GNOME/pygobject,jdahlin/pygobject,MathieuDuponchelle/pygobject,pexip/pygobject,davibe/pygobject