unstable(JRUBY-4171,linux,intermittent failure):IO.popen writes to a write-only pipe
fails:IO.popen starts returns a forked process if the command is -
fails:IO.popen does not throw an exception if child exited and has been waited for
fails:IO.popen with a leading ENV Hash accepts a single String command with a trailing Hash of Process.exec options, and an IO mode
fails:IO.popen with a leading ENV Hash accepts an Array command with a separate trailing Hash of Process.exec options, and an IO mode
