A negative uid value means it's not a "local socket" (PF_LOCAL).
uid==0 means user "root" connected.

Must return -1 on error, not 0.  0 is root.

Use the new uri_get_suffix() overload that removes the query string.

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!

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

Fixes buffer overflow bug.

There's always the "PCM" decoder plugin, which was never checked by
configure.ac.

MPD can easily be used as a database provider for the proxy database
plugin.  In that case, it needs only one "null" output, and no real
output plugin.

Allow building a smaller MPD binary for people who don't need DSD.

The name "cue" was listed twice in "mpd --version".

EXIT_SUCCESS and EXIT_FAILURE are defined in stdlib.h, not unistd.h.
D'oh!

Fixes MixRamp breakage.

On NetBSD, PTHREAD_MUTEX_INITIALIZER and PTHREAD_COND_INITIALIZER are
not compatible with C++11 "constexpr" (see Mantis ticket 0004110).  As
a workaround, don't ues "constexpr", and use the functions
pthread_mutex_init(), pthread_mutex_destroy(), pthread_cond_init() and
pthread_cond_destroy() instead.  This adds some runtime overhead, but
is portable to POSIX implementations that have awkward initializer
macros.

That attribute was uninitialized before, which could crash
libavformat.

See Debian bug 760669

See code comment.  Fixes assertion failure in
decoder_command_finished().