* Fix#811: new socket server to receive pid and port for subprocesses
* Install test dependencies from test_requirements.txt on Travis
* Multiproc support can't handle os.fork() as implemented.
On Python 3.4+, use set_start_method('spawn') to ensure that multiprocessing module doesn't use fork.
On lower versions, skip the test.
* Restrict the multiprocessing test to Windows for now.