merge revision(s) r43148,r43149,r43152: [Backport #8433]

	* thread.c (terminate_atfork_i): fix locking mutexes not unlocked in
	  forks when not tracked in thread.  [ruby-core:55102] [Bug #8433]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@45049 b2dd03c8-39d4-4d8f-98ff-823fe69b080e