topic-revset: changectx creation in the revset The current mutability filter is very expensive, we use a more direct and efficent way to do so: Before: ! wall 0.213261 comb 0.210000 user 0.210000 sys 0.000000 (best of 45) After: ! wall 0.012195 comb 0.020000 user 0.020000 sys 0.000000 (best of 217)