* gc.c: change oldmalloc meaning.
  Increase oldmalloc_increase with malloc_increase
  instead of using obj_memsize_of().
  This change will avoid the danger of memory full without major GC.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44040 b2dd03c8-39d4-4d8f-98ff-823fe69b080e