rb-site had a fairly outdated list of dependencies to check. Some of

these didn't matter and never showed up in the instructions (sqlite3

support, which is part of Python, and python-memcached, which we have

as a required dependency). A couple others are still relevant, but the

original packages providing the module have since been forked and

renamed.
This change trims down the module list to what's relevant today, and

enhances them with package names so that we can tell the user what to

run in order to get the support they need.

Ran through rb-site install, with missing modules. Saw the instructions

for installing them.