Abort if --enable-libmpdclient or --enable-upnp are used with
--disable-database, instead of ignoring the mismatch silently.

Fixes memory leak because ao_plugin_close() never gets called.

Be consistent.

A mutex acts as a memory barrier, and thus "volatile" is not
necessary.

Use the "_format" parameter instead of the (uninitialized) "format"
attribute.

Report unsupported format while opening the filter, not later when the
first conversion takes place.

Fixes assertion failure in destructor by not assigning
{src,dest}_format when an error occurs.

Fixes truncated lines in m3u and cue files (regression by commit
67958f7f).

The file systemd/mpd.service.in is being distributed implicitly, but
systemd/mpd.socket is not and needs to be added to EXTRA_DIST.

Fixes deadlock bug in the "mms" plugin.

Export it from the protected base class.  This fixes a build failure
on Mac OS X.

Fixes buffer overflow bug.

MPD handles all strings in UTF-8 internally.  Those decoders which
read Latin-1 tags are supposed to implement the conversion, instead of
passing Latin-1 to TagBuilder::AddItem().  FixTagString() is simply
the wrong place to do that, and hard-coding Latin-1 is kind of
arbitrary.

Share the NFS connection with the NFS input plugin.