Support of "unique contacts" for the new API
fbpost: queueing of facebook comments didn't worked at every time.
privacy_image_cache: avatar pictures of wall-to-wall-posts are now cached as well. And it is cached now at only one location
twitter: Repeating twitter items now does a native twitter retweet
Merge pull request #172 from annando/master

Unique contacts, bugfix in fbpost and better handling of avatars and cached data in privacy_image_cache