merge revision(s) r47818,r47832: [Backport #9820]

	* signal.c (rb_f_kill): should not ignore signal unless the
	  default handler is registered.  [ruby-dev:48592] [Bug #9820]

	* signal.c (rb_f_kill): get rid of deadlock as unhandled and
	  discarded signals do not make interrupt_cond signaled.
	  based on the patch by Kazuki Tsujimoto at [ruby-dev:48606].
	  [Bug #9820]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47956 b2dd03c8-39d4-4d8f-98ff-823fe69b080e