Log Message:
Updated musicpd to 0.20.4.

ver 0.20.4 (2017/02/01)
* input
  - nfs: fix freeze after reconnect
* output
  - sndio: work around a libroar C++ incompatibility
* workaround for GCC 4.9 "constexpr" bug
* fix FreeBSD build failure

ver 0.20.3 (2017/01/25)
* protocol
  - "playlistadd" creates new playlist if it does not exist, as documented
* database
  - proxy: fix error "terminate called after throwing ..."
  - proxy: make connect errors during startup non-fatal
* neighbor
  - upnp: fix premature expiry
* replay gain: don't reset ReplayGain levels when unpausing playback
* silence surround channels when converting from stereo
* use shortcuts such as "dsd64" in log messages