Slow pushes due to branch analysis
This is a follow-up to #351 (closed): analysis of branch/topic combinations can be very slow because it needs to correct the branchmap for obsolescence after the fact, since Mercurial core does not take it into account in versions less than 6.1.
For instance, we see an overhead of 3-4 seconds per active topic on mercurial/mercurial-devel>, with a resulting total push time bigger than 1 minute.
Early testing done on Mercurial 6.1rc, for which the branchmap correction becomes useless, is very positive.