Technically, these samples are signed.  There was no practical
difference, only the declaration was formally wrong.

Since we don't use OPEN_2CH_MAX, this should be equal to
WavpackGetNumChannels() - but who knows, maybe a future libWavPack
version breaks this assumption.

Enable OPEN_DSD_AS_PCM if available.  No OPEN_DSD_NATIVE yet.

 https://bugs.musicpd.org/view.php?id=4606

Use MPD's internal APE tag code, which works just as well.  This
removes some duplicate code for reading tags and ReplayGain.

MPD uses a floating point range from -1 to +1 internally - why ask
libwavpack to use -32768..+32768 only to reduce it back to -1..+1
afterwards?

It's wrong to use std::system_category() for both GetLastError() and
errno on Windows.  Apparently, everybody uses std::generic_category()
for errno values, which appears to be a safe choice.

Some discussion on this confusing topic can be found here:

 https://stackoverflow.com/questions/28746372/system-error-categories-and-standard-system-error-codes

Obsoletes the same variable from AudioConfig.cxx.

 https://bugs.musicpd.org/view.php?id=4595

Don't use the global variables in class DecoderBridge; instead,
forward these values to the decoder thread via PlayerControl and
DecoderControl.

Declare two named elements.  An enum should not be used as an array
index, as this is error prone.

Speed up container_scan() again, by eliminating the need to call
scan_file() for each item.

Broken by commit 0abee77e

Got lost in 0abee77e

Catch ENOTDIR exceptions and in that case, try all matching decoder
plugins which implement the "container_scan" method.

 https://bugs.musicpd.org/view.php?id=4561