Load APE/ID3 tags from archives.

This commit adds support for APE/ID3 tags from NFS/SMB files.

See http://bugs.musicpd.org/view.php?id=4270

Fixes deadlock.

release v0.19.13

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.

decoder_load_replay_gain() will create the InputStream anyway, so
we're not saving any overhead by opening the InputStream on demand
only.

Prepare for APE tag support on userspace NFS/SMB/CIFS mounts.

Prepare for ID3 support on userspace NFS/SMB/CIFS mounts.

Use a 128 byte buffer instead of reading 10 bytes first and then 118.

The check was added in commit 98fd9b7d, but there was never a
definition.