Dev/fixprecise

Currently `apt-get install dsc12` fails on Ubuntu 12.04 because `apt-get` only sees `cassandra=2.0.1` by default and doesn't know what to do about a requirement to install `cassandra=1.2.10-1`. I've added a conditional to the recipe to preemptively install the correct version of the cassandra package on Debian machines.

I've laso changed the datastax repo URLs to use HTTPS.