Comment 3 for bug 991033

Created attachment 617120
fix a few issues

This fixes a bit rot issue with the previous patch, and makes uploading files that we don't know the mime type of work (it was failing because the code wasn't catching the exception, so I've fixed that). I've also fixed the offline error to use throw.

With those changes, I was able to sign up for a UbuntuOne account and send a filelink, so the basics seem to work.