support cloud storage, and assorted other improvements

I just finished support for fdroid server update to push to Amazon AWS S3 cloud store. It uses libcloud, so there could be lots of other cloud storage services added. This would be used for alternative hosting locations for repos. For example, for the Guardian Project repo, we'd include the URLs to various cloud storage options like https://s3.amazonaws.com/guardianproject/fdroid/repo Services like https://s3.amazonaws.com/ are often not blocked when other things are.

It does not need to be Amazon-specific. I went with libcloud because it supports like 10 cloud storage and is under active development. What is there is just the start. I'm new to cloud stuff, so I just started based on a script that Adam Prichart of psiphon gave me. I had to do a fair amount of packaging work to get the python-libcloud Debian package updated. I almost have the 0.14.1 update done, I hope that'll be in Debian tonight.

Lots more info in the commit messages.

This all looks cool. The main problem I have is that libcloud becomes a hard requirement to do anything, even though it supports an optional feature. Could that be resolved just by moving the import inside the relevant function?

Yup, I fixed that. The imports are now all within update_awsbucket() in server.py