* Try .bin when opening a .cue, instead of trying the filename in the .cue (it's usually wrong).
  When the .bin filename fails, then look into the .cue file for a possible alternate name.
* Don't crash on non-existing cuefile's

I would like to backport some of this, but 0.8.6 doesn't have utf8_open, so I need to see what i'm gonna do with that.