botan: additional openssl dependency

Added OpenSSL dependency, added a Python dependency for the older systems to try and support those a little better, and double quotes everywhere. The download location has also moved upstream. Any attempt to use the old one just gets a redirect to the new one, so I’ve just switched it. For some reason the checksum has changed, but the pgp signature for the download file was verified fine, so *shrug*.
It's Python 2.6 > required here. I'll remove it. We can always come back to it if downstream bump their Python requirement.