merge revision(s) 39276: [Backport #7825]

	* vm.c (rb_thread_mark): mark a working Proc of bmethod
	  (a method defined by define_method) even if the method was removed.
	  We could not trace working Proc object which represents the body
	  of bmethod if the method was removed (alias/undef/overridden).
	  Simply, it was mark miss.
	  This patch by Kazuki Tsujimoto. [Bug #7825]
	  NOTE: We can brush up this marking because we do not need to mark
	  `me' on each living control frame. We need to mark `me's
	  only if `me' was free'ed. This is future work after Ruby 2.0.0.

	* test/ruby/test_method.rb: add a test.


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/branches/ruby_1_9_3@44736 b2dd03c8-39d4-4d8f-98ff-823fe69b080e