Add test for previous core dump when sending on closed socket with timeout.
Add test for previous core dump when sending on closed socket with
timeout.

Added small sleeps to _testAccept() and _testRecv() in
NonBlockingTCPTests, to reduce race conditions (I know, this is not
the solution!)

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