UPDATE: add HACK to allow scrobbling

Added fictional duration to songs as a HACK to enable scrobbling

* scrobbling doesn't work with the current XBMC core player unless the
  'duration' field of the song info is set to a positive number prior to
  starting the song (even though the song duration will be correct in the player)
* with no 'duration' (or 0 or -1), last.fm is notified of  the song playing but
  never receives the final scrobble notification to add it to the history
* BUG: the HACK does cause the core player to see/display an incorrect total
  song time (although the progress/duration bar is visually correct)

NOTE: scrobbles may be cached until the Pandora script is halted and then submitted en mass

NOTE: (see URLref: http://www.last.fm/api/scrobbling) for scrobble info