* ext/pty/pty.c (pty_check): should return nil until the child
	  terminates or stops.  [ruby-dev:44600] [Bug #2642]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34183 b2dd03c8-39d4-4d8f-98ff-823fe69b080e