6.1.2 media absolute urls

This is to allow media items to be stored with absolute URLs like: https://s3-eu-west-1.amazonaws.com/gibedigital/1012/tosc-042013.jpg

For use with CDNs and block storage, this allows new FileSystemProviders that don't write to any physical location on the server. Currently they error at cehttps://s3-eu-west-1.amazonaws.com/gibedigital/1012/tosc-042013.jpg

The full discussion is here:
https://groups.google.com/forum/#!topic/umbraco-dev/GjToBgs0mHk