mpd: Remove Python 2.6-ism
mpd: Format search query regexps better
mpd: Accept 'albumartist' type to 'find' and 'search' commands
mpd: Map 'albumartist' field from MPD to Mopidy query
mpd: Don't return fake artists when searching by albumartist
mpd: Review fixes
Merge branch 'develop' into feature/mpd-search-by-albumartist

Conflicts:
	mopidy/frontends/mpd/protocol/music_db.py
	mopidy/frontends/mpd/translator.py
Merge pull request #551 from jodal/feature/mpd-search-by-albumartist

Add search and find by albumartist to MPD frontend