* gc.c (is_before_sweep): Add new helper function that check the object
	  is before sweep?
	* gc.c (rb_gc_force_recycle): Have to clear mark bit if object's slot
	  already ready to mainor sweep.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41633 b2dd03c8-39d4-4d8f-98ff-823fe69b080e