atk/atkaction.c, atk/atkcomponent.c Remove all instances of

atk/atkaction.c, atk/atkcomponent.c Remove all instances of

* atk/atkaction.c, atk/atkcomponent.c
Remove all instances of g_return_if_fail (foo != NULL); that are
immediately before a g_return_if_fail (ATK_IS_FOO (foo));
since the second check catches the NULL.
* atk/atkcomponent.c
Add functions atk_component_real_contains(),
atk_component_real_get_position(), atkcomponent_real_get_size()
as default implementations for atk_component_contains(),
atk_component_get_position(), atk_component_get_size()