Add better RSS parsing support for podcast discovery

As requested in: http://forum.videolan.org/viewtopic.php?f=14&t=62846

VLC does open many podcast RSS URLs but not all. Some URLs that don't work cause strange gibberish messages that aren't very nice.

Sample URL: http://pointofinquiry.libsyn.com/rss

Which currently causes something like http://imgur.com/z1tuf.jpg