When a previous call to poll() has already seen the process status, wait() should not call waitpid() again.
When a previous call to poll() has already seen the process status,
wait() should not call waitpid() again.

Should be backported to 2.2.4.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator