Dynamically discoverd the size of the ioinfo struct used by the crt for its file descriptors.  This should work across all flavors of the CRT.  Thanks to Amaury Forgeot d'Arc
Needs porting to 3.1

import lock if called from within a thread that was triggered by an import.

Partially fixes issue #1665206.

exactly one pattern, which avoids mysterious errors where it
had seemed to fail to do localization.

correction in a previously fixed test.

after closing the socket.