Enhance type recognition upon playlist import

[Mathias Brodala]

The function xl.playlist.import_playlist already handles some corner cases but can be improved. For example the following playlist will be unrecognized:

http://yp.shoutcast.com/sbin/tunein-station.pls?id=32453

This is due to gio.content_type_guess() returning "application/octet-stream", thus failing and simple extracting of the file extension results in "pls?id=32453", thus also failing. We cannot do anything about the first but fix the second via urlparse.

Additionally a third, most expensive, method should be added which uses gio.FileInfo.get_content_type(). Since this way the data needs to be loaded before inspection, it should be the last resort before giving up.

[Mathias Brodala (mathbr)]

Fixed with r4000. (Not yet over 9000, sorry)