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.

Fixes deadlock on small responses.

The Connect method can be called between Schedule and lock. In that case, when
locked, the state is already set to CONNECTING of READY and the condition won't
be signaled anymore.

Not initialising granulepos leads to it having arbitrary values in the
encoded stream including possibly negative values which are not valid
and confuse opusdec.  Explicitly initialise opus_encoder::granulepos
to avoid that problem.

The file handle is never reset to INVALID_HANDLE_VALUE, and thus the
destructor will assume the operation shall be cancelled and will
delete the temporary file.

This was a major breakage for saving the database file and the state
file.

Build a table of pre-existing tag types before adding new items.  The
old way would check HasType() each time, which would return true after
the first instance of that tag type had been added, preventing
duplicate tag types to be merged.

This broke duplicate tag types loaded from the state file, because
this code path uses TagBuilder::Complement().

Apparently, Android's build.xml requires the icon to be available,
even when only running the Java compiler.

std::auto_ptr is deprecated, and std::unique_ptr is much better
anyway.