cmdutil: stop pretending we can calculate revs for graphlog lazily
cmdutil.getgraphlogrevs does a ton of work trying to build a graphlog lazily,
and then cmdutil.graphlog comes along and destroys all of that.
graphmod.dagwalker requires that it be given the full list of revs upfront so
that it can perform filtering and tests against known revs.
For a repository with over 400,000 changesets, this speeds up graphlog by
around 0.02 seconds (~20% with a small limit).