As it turns out, the things returned by Winsock2's socket() are handles
that can be passed to ReadFile()/WriteFile() - almost. The way this works
is by wrapping those handles into file descriptors with _open_osfhandle().
But it turns out that the sockets created by the plain socket() function
are prepared for "overlapped" I/O, which confuses ReadFile()/WriteFile().
Therefore, a reimplementation is provided that uses WSASocket() to
explicitly asks for non-overlapped sockets.
Special thanks got to H. Peter Anvin, who provided the necessary clues.
