* gc.c (RGENGC_CHECK_MODE): separate checkers to different modes.
  * 2: enable generational bits check (for debugging)
  * 3: enable livness check
  * 4: show all references



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44112 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* gc.c (allrefs_add): push obj only if allrefs table doesn't have
  obj.
* gc.c (allrefs_roots_i): ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44113 b2dd03c8-39d4-4d8f-98ff-823fe69b080e