Issue 2550: extend test_socket.py to test SO_REUSEADDR semantics when bind() is calle...

Issue 2550: extend test_socket.py to test SO_REUSEADDR semantics when bind() is called on identical (host, port) combinations in two separate sockets.  This should raise an EADDRINUSE socket.error in all cases, irrespective of whether or not SO_REUSEADDR is set on the sockets.  However, with Windows, when SO_REUSEADDR is set on the sockets, no error is thrown (an error is thrown when the option isn't set), which results in an extremely wedged python process whenever accept() is called on either of the bound sockets.  I'm committing this test now to observe if it's only Windows that has this behaviour (via the buildbots).  Note: this WILL break all Windows buildbots for now; once I've observed the results on other platforms, I'll revert, then start looking into a patch.