Extend 020-reviewrebase.py to test the [partial] filter a little

This tests that the "Fix crash when using [partial] filtering on rebased
review" commit in r/207 does its job correctly.
Change URLs to point to https://critic-review.org/

The system now enforces HTTPS.  It also redirects all HTTP requests to
HTTPS, so the old URLs works absolutely fine, but best to link to HTTPS
directly.