merge revision(s) 46194: [Backport #9835]

	* signal.c (signal_exec): ignore immediate cmd for SIG_IGN

	* signal.c (trap_handler): set cmd to true for SIG_IGN

	* signal.c (trap): handle nil and true values for oldcmd
	  [Bug #9835]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@46575 b2dd03c8-39d4-4d8f-98ff-823fe69b080e