threads are still running.  Instead, reinitialize the GIL on a second
call to Py_Initialize().

PyThread_create_key now has a failure mode that the applicatino can detect.

fromlist to get __import__ to return the module desired. Now it uses the proper
approach of fetching the module from sys.modules.

Closes issue #9252. Thanks to Alexander Belopolsky for the bug report.

recv() and send()

non-blocking mode: they return None when an operation would block (instead
of raising an exception).