* gc.c: remvoe ruby_disable_gc_stress and add ruby_disable_gc
  to speed-up newobj_of().
* gc.c (ready_to_gc): check ruby_disable_gc.
* signal.c: use ruby_disable_gc.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47465 b2dd03c8-39d4-4d8f-98ff-823fe69b080e