* gc.c: continue to change OLDSPACE -> OLDMALLOC.
  RGENGC_ESTIMATE_OLDSPACE -> RGENGC_ESTIMATE_OLDMALLOC.
* gc.c: add a new major GC reason GPR_FLAG_MAJOR_BY_OLDMALLOC.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43837 b2dd03c8-39d4-4d8f-98ff-823fe69b080e