performance: speedup computation of suspended revisions In their current state, revset calls can be very costly, as we test predicates on the entire repository. This change drops a revset call in favor of direct testing of the phase of changesets. Performance test on my Mercurial checkout - 19857 total changesets, - 1584 obsolete changesets, - 13310 obsolescence markers. Before: ! suspended ! wall 0.014319 After: ! suspended ! wall 0.009559 Performance test on a Mozilla central checkout: - 117293 total changesets, - 1 obsolete changeset, - 1 obsolescence marker. Before: ! suspended ! wall 0.033373 After: ! suspended ! wall 0.000053