* subcompositor.c (ViewMap, ViewUnmap): Union view inferior
bounds whenever possible, instead of garbaging the
subcompositor.
* tests/subsurface_test.c (enum test_kind): New test
`SUBSURFACE_STACKING_1_KIND'.
(test_names): Add new name.
(LAST_TEST): Set to SUBSURFACE_STACKING_1_KIND.
(test_single_step): Implement SUBSURFACE_STACKING_1_KIND.
* subcompositor.c (DoCull): Fix leak of temp region upon
encountering opaque view.
* tests/subsurface_test.c (enum test_kind, test_names): New test
SUBSURFACE_GROW_SHRINK_KIND.
(LAST_TEST): Make it the last test.
(test_single_step): Implement SUBSURFACE_GROW_SHRINK_KIND.