Fixes disappearing duration of remote songs during playback.

See http://bugs.musicpd.org/view.php?id=4492

The initgroups() manpage says we need to check for _BSD_SOURCE.  The
thing is that glibc deprecated this macro, and doesn't define it
anymore, effectively breaking all MPD supplementary groups.

The real fix is to check for initgroups() availability at configure
time, instead of relying on the deprecated _BSD_SOURCE macro.

Apply padding only to the fseek(), not to the chunk size.  This fixes
bogus "failed to read riff chunk" messages when the last chunk has an
odd size.

See http://bugs.musicpd.org/view.php?id=4486

These are other popular clients. In particular, VLC is available on
mobile devices.
Signed-off-by: Ben Boeckel <mathstuf@gmail.com>

systemd does not understand LimitRTTIME=-1. For no limit we have to use
the string 'infinity' (see systemd.exec(5)).
Signed-off-by: Christian Hesse <mail@eworm.de>

Add ALSA_LIBS to MIXER_LIBS, otherwise building mpd in a static context fails
with lot of undefined references to alsa-lib (libasound) required by
src/mixer/plugins/AlsaMixerPlugin.cxx.
Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>

This systemd feature has been removed a while ago without replacement,
and it turns out that systemd developers suggest not using control
groups at all to assign real-time privileges.  Therfore, a replacement
feature will not be implement in future systemd releases, and we can
really remove those lines completely.

See http://bugs.musicpd.org/view.php?id=4413

Fixes http://bugs.musicpd.org/view.php?id=4432

Fixes mixer lag (http://bugs.musicpd.org/view.php?id=4425).

Allocate the buffer dynamically using av_malloc(), and free
AVIOContext.buffer in the destructor, as mandated by the libavformat
documentation.

Fixes http://bugs.musicpd.org/view.php?id=4446

Eliminates some duplicate code, and as a side effect, this works
around clang 3.8 compiler warning because a negative value was
shifted.

Copy to encoder->audio_format *after* adjusting the sample format to
S24_P32.

Fixes http://bugs.musicpd.org/view.php?id=4433

Fixes missing SongBorder() call, which causes "single" mode breakage.

If there's a stream tag, don't let the song tag override it in the
next update_stream_tag() call.

If the song tag comes from a stream, and MPD playback restarts, MPD
would believe the tag should override the newly received tag.  This
makes the previous tag appear stuck.  This change passes the song tag
only if it's authoritative - i.e. if it's a song file.

Reduce runtime overhead.

Right after booting, the monotonic clock starts with a very small
value, and AudioOutput::LockUpdate() may believe that the fail_timer
has not recovered yet.

When seeking to the beginning of a packet, skip the samples that come
before the desired time stamp.

Ask FFmpeg to seek to the next packet boundary *before* the seek
position, so we don't miss audio data.  Now we get too much, but we'll
solve that in the next commit.