Bug #477708. Only remove the target, not the relation if there are still

Bug #477708. Only remove the target, not the relation if there are still

2008-11-10  Li Yuan  <li.yuan@sun.com>

        * atk/atkobject.c: (atk_object_remove_relationship):
        Bug #477708. Only remove the target, not the relation if
        there are still are targets.
        * atk/atkrelation.c: (atk_relation_remove_target):
        * atk/atkrelation.h: New API.
        * atk/atkrelationset.c: (atk_relation_set_add),
        (atk_relation_set_remove):
        Add/remove the new relation's targets to/from the existed
        relation if there has been a relation with the same type.
        * atk/atkstateset.c: (atk_state_set_or_sets):
        Bug #478595. Return NULL if sets are empty.

svn path=/trunk/; revision=1297