subclasses of SystemCallError.  in addition, if initialize is
  called for SystenCallError instance, its class be changed.
  [ruby-dev:20257]

* gc.c (run_final): to protect thread context switch, finalizers
  are wrapped in DEFER_INTS/ENABLE_INTS.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@3839 b2dd03c8-39d4-4d8f-98ff-823fe69b080e