Python os.waitpid throw `[Errno 10] No child processes`
<p>Following code return with <code>[Errno 10] No child processes</code> on windows platform (python version 2.7.2).</p>

<pre>
import subprocess
import os
pid = subprocess.Popen(["cmd"]).pid
os.waitpid(pid, 0)
print 'process %d finished' % pid
</pre>

<p>The same code works well on Linux.</p>
