if we are asking for a prerelease, we should run the same comparison as normal

Previously, if we were asking for a pre-release, we would only return true if it was the
same pre-release, or at least on the same release. But that's not true. 1.2.4 should be valid
if we want 1.2.4-rc0, for example, and, even 1.2.3-rc0. (I mean, if it has the same ecv, which
it might not). This is also what was causing some of the issues around 0.9.1 rollout, we think. So,
we are going to try treating rcs like normal versions as far as comparisons go. We still don't want to
give you an rc unless you asked for it though.
fix the test for updating RCs and make list tell you about new rcs sometimes

1. Fixes the test for updating to a new rc. First, change the ordering -- since we order RCs now, it means that if you add rc.3 while
rc.4 is available it just adds rc.4. So, now, we publish rc.4 after rc.3 has been added, run update (with the right options) and
check that it worked.

2. When you run list, we check if there are newer versions of packages. Usually we just look at mainline versions. But if you are already
using an rc version of a package, you might care about new rcs too. So, in that case, we check the latest of *all* available versions.