Fix url path get encoded twice

Hey Daniel,

i had an problem to download files embedded in the feed were the url is already urlencoded. 

Reproduce the Problem:

1. add a new Podcast the "Android Developers Backstage" Podcast from gpodder.net
2. try to download an episode from this podcast
3. the Download failed with a 404

The Problem is in [src/de/danoeh/antennapod/service/download/HttpDownloader.java#L32](https://github.com/danieloeh/AntennaPod/blob/master/src/de/danoeh/antennapod/service/download/HttpDownloader.java#L32)

You first create an URL and after that you are creating an URI with all the components of this created URL. By using the multi-argument constructor URI the path of the URL get urlencoded again.
See http://stackoverflow.com/questions/4858108/url-to-uri-encoding-changes-a-3d-to-253d for details

regards,
David