Auto-discover media files in flashvars too

Songbird does a great job by finding and listing any playable media linked from the current website. We can then play those directly in Songbird.

But many websites bring their own flash player with them, so they embed a flash media player that plays back an mp3. Songbird should discover such audio files and offer them for direct playback, too. I think this is as simple as looking for anything that looks like a compatible file URL in the flashvars attribute of the embed tag.