So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

The number of MPD installs on Android < 5.0 is negligible, and that
API version introduces lots of useful features for MPD.

Fixes the NFS client build, closes #305.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

Apparently, connecting a socket to a loopback address can block on
Windows, and a non-blocking socket will return WSAEINPROGRESS.  This
broken PoorSocketPair() in commit 2119e4fd, which made the socket
non-blocking right from the start.  This fix postpones the
ioctlsocket(FIONBIO) call until after the connect().

Closes #134

It does not do much harm - but it causes an unnecessary (failing)
system call.