Rafactoring, RandomTrackNavigator

[Thomas Lübking]

I ran into an issue while testing the RandomTrackNavigator 
likelyNext/requestNext reimplementation.

When one reaches the end of the (unrepeated) playlist and skips bwd, one can 
no more skip fwd (the playback ends)
After spending some time on searching the bug in my code, i just compiled 
vanilla amarok and the behaviour is the same.

Personally, I'd consider this behaviour wrong (it should be as the 
replayed_tracks are not taken into consideration when testing for the next 
track. Aside this, the first previous track is the current one instead of 0L)

Is this behaviour intended or should I fix it while being at it anyway?

Cheers,
Thomas