merge revision(s) 40182,40221: [Backport #8311]

	test_curses.rb: add sentinel

	* test/test_curses.rb (TestCurses#run_curses): add sentinel to get rid
  of read pty output after the child process terminated, which causes
  EIO on Linux.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@40421 b2dd03c8-39d4-4d8f-98ff-823fe69b080e