* gc.c (slot_sweep_body): rename to slot_sweep().
  No need to separate major/minor GC.
* gc.c (gc_setup_mark_bits): remove gc_clear_mark_bits() and unify to
  this function.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41547 b2dd03c8-39d4-4d8f-98ff-823fe69b080e