Add support for MIME types / Content-Type headers via GIO. Add editor modelines.

[geraldcombs]

No description provided.

[tombh]

Damn, I've just gone and written something similar to this :( Teaches me for not checking the pull requests firsts!

Just for reference, I implemented my solution to get around the problem of using FTP on the mounted cloudfiles filesystem. What was happening was that FTP clients were writing their files to the filesystem in parts, where the first part triggered Rackspace's mime-type detection, which would inevitably be wrong as the whole file hadn't been copied yet. Therefore I changed cloudfuse to locally detect the mime-type when copying a file, thus resending the correct content-type to the cloudfiles object.