Fixes regression by commit 7c8038e2

Allow multiple targets to share a library directory tree.

setvbuf() does not seem to have an effect on Windows.

Make sure everything gets logged right away.  No delays because
stdio's buffer is not yet full.

Without MEM_COMMIT, the reserved address space is not accessible, and
MPD crashes.

The definition of the playlist_plugin struct member of the embcue
plugin was incorrect.

Works around assertion failure due to something that appears to be a
(minor) FFmpeg bug.

Fixes bogus assertion failure.

SocketMonitor::Cancel() does not actually unregister the socket; it
only disables the event.

When mounting had not yet finished, SocketMonitor::IsDefined() was
always false, due to the workaround at the beginning of the function
that calls SocketMonitor::Steal().  This commit drops the IsDefined()
check because it was never necessary and breaks reconnect.

nfs_destroy_context() will invoke all pending callbacks with
err==-EINTR.  In CancellableCallback::Callback(), this will invoke
NfsConnection::DeferClose(), which however is only designed to be
called from nfs_service().  In non-debug mode, this will leak memory
because nfs_close_async() is never called.

Workaround: before nfs_destroy_context(), invoke nfs_close_async() on
all pending file handles.