revset: optimize not public revset This patvh speeds up the computation of the not public() changeset and incidentally speed up the computation of divergents() changeset on our big repo by 100x from 50% to 0.5% of the time spent in smartlog with evolve. In this patch we optimize not public() to _notpublic() (new revset) and use the work on phaseset (from the previous commit) to be able to compute _notpublic() quickly. We use a non-lazy approach making the assumption the number of notpublic change will not be in the order of magnitude of the repo size. Adopting a lazy approach gives a speedup of 5x (vs 100x) only due to the overhead of the code for lazy generation.