Instead of just bootstrapping the algorithm with the first revision we
see, allow callers to pass revs that should be displayed first. All
branches are retained until we can display such revision.
Expected usage is to display the current working copy parent first.
The algorithm now works when some revisions are skipped. We now use "first
included ancestors" instead of just "parent" to link changesets with each other.
We add an experimental config option to use the topological sorting. I first
tried to hook the 'groupbranchiter' function in the 'sort' revset but this was useless
because graphlog enforces revision number sorting :(
As the goal is to advance on the topological iteration logic, I see this
experimental option as a good way to move forward.
We have to use turn the iterator into a list because the graphlog is apparently
not ready for pure iterator input yet.
