Negating an unsigned integer does not work.

Works around the "PCM conversion from f to dsd is not implemented"
error message that prevents DSD playback.

Many years ago, FAAD had a serious ABI bug: the NeAACDecInit()
prototype in its header declared the "samplerate" parameter to be
"unsigned long *", but internally, the function assumed it was
"uint32_t *" instead.  On 32 bit machines, that was no difference, but
on 64 bit, this left one portion of the return value uninitialized;
and worse, on big-endian, the wrong word was filled.  This bug had to
be worked around in MPD (commit 9c4e97a6).

A few months later, the bug was fixed in the FAAD CVS in commit 1.117
on file libfaad/decoder.c; the commit message was:

 "Use public headers internally to prevent duplicate declarations"

The commit message was too brief at best; the problem was not
duplicate declarations, but a prototype mismatch.  No mention of the
bug fix in the ChangeLog.

The MPD project never learned about this bug fix, and so MPD would
always pass a "uin32_t *" dressed up as a "unsigned long *".  Nearly 6
years later, it's about time to fix this second ABI problem.  Let's
kill the workaround!

MPD_PATH_MAX_UTF8 is only used by GLib-specific code currently.

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.