test_properties: Test accessing a property from a superclass
test_properties: Test accessing a property from a superclass

We already cover accessing the superclass' property if that was defined in
Python. Add a corresponding test case for a property defined in C.

See https://bugzilla.gnome.org/show_bug.cgi?id=684058

davibe/pygobject,pexip/pygobject,GNOME/pygobject,sfeltman/pygobject,pexip/pygobject,GNOME/pygobject,davibe/pygobject,davibe/pygobject,davibe/pygobject,sfeltman/pygobject,GNOME/pygobject,pexip/pygobject,sfeltman/pygobject