Log Message:
Updated musicpd to 0.19.20.

ver 0.19.20 (2016/12/09)
* protocol
  - "setprio" re-enqueues old song if priority has been raised
* decoder
  - ffmpeg: ignore empty packets
  - pcm: fix corruption bug with partial frames (after short read)
  - sidplay: fix playback speed with libsidplayfp
* output
  - winmm: fix 8 bit playback
* fix gcc 7.0 -Wimplicit-fallthrough
* systemd: paranoid security settings