* gc.c: count young object correctly and show it in GC.stat
  on RGENGC_AGE2_PROMOTION.
* gc.c (RVALUE_PROMOTE_YOUNG): decrement young object count on
  YOUNG->OLD.
* gc.c (obj_free): decrement young object count when young object
  freed.
* gc.c (gc_marks): should not clear young object count.
* gc.c (gc_stat_internal): GC.stat :young_object information.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45925 b2dd03c8-39d4-4d8f-98ff-823fe69b080e