Plugin to support importing updates from external RSS and Atom feeds into your timeline.

Uses PubSubHubbub for push feed updates; currently non-PuSH feeds cannot be subscribed.

Todo:
* set feed icon avatar for actual profiles as well as for preview
* use channel image and/or favicon for avatar?
* garbage-collect subscriptions that are no longer being used
* administrative way to kill feeds?
* functional l10n
* clean up subscription form look and workflow
* use ajax for test/preview in subscription form
* rssCloud support? (Does anything use it that doesn't support PuSH as well?)
* possibly a polling daemon to support non-PuSH feeds?
* likely problems with multiple feeds from the same site, such as category feeds on a blog
  (currently each feed would publish a separate notice on a separate profile, but pointing to the same post URI.)
  (could use the local URI I guess, but that's so icky!)
* problems with Atom feeds that list <link rel="alternate" href="..."/> but don't have the type
  (such as http://atomgen.appspot.com/feed/5 demo feed); currently it's not recognized and we end up with the feed's master URI
* make it easier to see what you're subscribed to and unsub from things
* saner treatment of fullname/nickname?
* make use of tags/categories from feeds
* update feed profile data when it changes
* XML_Feed_Parser has major problems with category and link tags; consider replacing?