* gc.c (gc_before_sweep): cap `malloc_limit' to
  gc_params.malloc_limit_max.  It can grow and grow with such case:
    `loop{"a" * (1024 ** 2)}'
  [Bug #9687]
  This issue is pointed by Tim Robertson.
  http://www.omniref.com/blog/blog/2014/03/27/ruby-garbage-collection-still-not-ready-for-production/



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45468 b2dd03c8-39d4-4d8f-98ff-823fe69b080e