* gc.c: do major/full GC when:
* number of oldgen object is biggger than twice of
  number of oldgen object at last full GC.
* number of remembered shady object is bigger than twice of
  number of remembered shady object at last full GC.
* number of oldgen object and remembered shady object is bigger
  than half of total object space.
  (please fix my English!)



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40914 b2dd03c8-39d4-4d8f-98ff-823fe69b080e