Added support for playqueue-contents with negativ span value (returns the previously played songs)
fixes for playqueue-contents
fixup indentation
Remove dead code: playback_next_bh and playback_prev_bh are only called
during playback_pause. In playback_pause "cur_playing" is always set to
NULL so that in playback_next_bh and playback_prev_bh only the
else-clause can become true.
Indentation
Merge playqueue-contents from chme (support for history)