Allow running sptps_test on Windows

Allow running sptps_test on Windows

On Windows, you're not supposed to call select() on anything except
proper BSD sockets, so we can't reuse the same select() loop that's been
working fine on every other operating system.

This is a hack which reads stdin in a separate thread and pushes data to
the main through a TCP socket, which can then be used with select() instead
of reading stdin directly.