Fixes two build failures with libnfs on Windows.

configure.ac sets this, but this wasn't used for compiling third-party
libraries.  This setting however is important for libnfs, which adds
fallback definitions for POLLIN and POLLOUT with bogus values.

It indeed is a macro on Windows.

Instead of setting state=IGNORE_TRACK, ignore only the following
"INDEX" lines.

Correction for commit 8461d71b.  Closes #227

Let FFmpeg do the MP3 decoding.  See commit
a4de9650

Closes #232

libmad has been unmaintained for a long time, and it fails to build on
Windows.  I could go and fix libmad's broken configure script, but I
prefer to just assign MP3 decoding to FFmpeg for now.

Closes #228

Enable the NFS storage plugin on Android.

Closes #226

This addresses two problems:

1. the libFLAC write callback had to send an error status to its
caller when SubmitData() returned a command; this disrupted libFLAC
and the resulting command could not be used for anything;

2. the libFLAC function FLAC__stream_decoder_seek_absolute() also
calls the write callback, but its result cannot be used, because
seeking is still in progress, so we lose all data from one FLAC frame.
By moving the SubmitData() call until after CommandFinished(), we
avoid losing this data.  This fixes another part of #113

See code comment.

Instead of passing whole chunks to the MusicPipe and checking the
end_time after each chunk, truncate the last chunk if it would exceed
the end_time.  This requires keeping track of the absolute PCM frame
number.

This fixes a problem with gapless CUE song transitions: a small part
of the following song was always played twice.

Closes #113

it was uninitialized before

Due to rounding errors, a slightly negative value can be passed to
set_normalized_volume(), which will make the log10() call fail.
Actually, volume 0 is already failing because log10(0) is illegal.  So
let's fix this by implementing two corner cases: <=0 and >=100.

Closes #212

Closes #213.

Apparently, clang defaults to NEON when ARMv7 is used.  Not all ARMv7
CPUs we target have NEON, so we need to disable that.

Not needed on Android, and the implementation uses getpwuid_r() which
is unavailable on old Android versions.

Requires Android API 21, but we want to support older versions as
well.

For Android pre-5.0 compatibility (#213).

For Android pre-5.0 compatibility (#213).

For version numbers such as OpenSSH's, e.g.: "7.2p2"

Closes #217

Fixes valgrind warning.

This was a buffer overflow bug which could cause MPD crahes when
playing back 8 channels with the ALSA output plugin.

Closes #216

There is a POSIX definition for sched_setscheduler(), but Linux does
not implement that; instead of changing the process's scheduler, it
only affects one thread.  This has caused some confusion among
application developers and C library developers.

While glibc implements Linux semantics, Musl has made their
sched_setscheduler() function an always-failing no-op, causing the
error message "sched_setscheduler failed: Function not implemented".

 http://git.musl-libc.org/cgit/musl/commit/src/sched/sched_setscheduler.c?id=1e21e78bf7a5c24c217446d8760be7b7188711c2

Instead of relying on the C library which may be unreliable here, we
now roll our own system call wrapper.

Closes #218