ControlDecoration doesn't work on GTK 3.14: the decorations are not
visible at all.

During fixes of regressions caused in Bug 531667, we observed that one
of the fixes can also be applied to GTK 3.14 to restore
ControlDecoration functionality.

Snippet Bug531667_Group_drawing_with_paint_listener_is_wrong can be used
to examine results before and after patch.

Change-Id: I7243c366c5bc0a90ada4a37d689c241493361c10
Signed-off-by: Simeon Andreev <simeon.danailov.andreev@gmail.com>