reshuffle only songs in the UpNext queue
clear queue on playback abort
Ignore queuefilter on playqueue-edit-add if mode = 0 (add to up next)
Use query parameter if queuefilter parameter is unkown
Fix segfault on reshuffling one item
If reshuffling with repeat all songs in queue active, set shuffle-head
to current playing song. Previously the shuffle-head was set to the next
song after the current, therefor the UpNext-queue appeared empty after
adding new songs to the queue.
Merge pull request #39 from chme/playqueuefix

Fixes for UpNext playqueue