merge revision(s) 40534,41886,41903,41910: [Backport #8616]

	process.c: rb_daemon should not raise

	* process.c (rb_daemon): should not raise exceptions, since
  proc_daemon() will deal with errors.
	* process.c (fork_daemon): kill the other threads all and abandon the
	  kept mutexes.

	* process.c (fork_daemon): kill the other threads all and abandon the
	  kept mutexes.

	* process.c (rb_daemon): daemon(3) is implemented with fork(2).
	  Therefore it needs rb_thread_atfork(). (and revert r41903)


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@43142 b2dd03c8-39d4-4d8f-98ff-823fe69b080e