pylint tweaks
remove redundant [elapsed, remaining] parameter
pylint tweaks
do not rely on leaking loop variable

- do not rely on leaking loop variable; e.g.:
  'for self.foo in  ...' => 'for tmp in ...'
- remove fix_url(), appears to be a no-op.
- only add valid songs
change players: ditch mppdec; promote mplayer; add gst123

- ditch 'mppdec' as it was part of a previous version of the musepack
  format. the new command mpcdec does not play audio files but only
  decodes to wave; mpc123 does not support seeking.
- promote 'mplayer' over other players that do not support seeking.
- add gst123; via http://github.com/xi/cplay-ng
  TODO: autodetect file formats supported by gstreamer.