Remove tempfile when hash verification fails
Drop EL < 6 support

This will make it easier to move away from md5 for the source tarballs.

It shouldn't cause any problem anyway, as Fedora runs this on EL 6.
Rename some variables and comments away from md5

We are moving away from using md5 for the uploaded source tarballs, so
the code shouldn't be full of assumptions that everything is md5 any
more.
Add support for sha512 file hashes

With this change, the upload CGI script will start preferring uploads
hashed as sha512, but still accept md5 as a fallback.

https://fedorahosted.org/rel-eng/ticket/5846
lookaside: Make the hash type part of the folder structure

This makes it more explicit which hash was used for a given tarball.