evolve: improve the help message of --rev User's are not exposed to the notion of revset, this patch makes the help message more intelligible.

evolve: add --rev option to the evolve command This patch is part of a series of patches to refactor the evolve method and make it more readable. We introduce a new --rev flag to specify a revset where to solve the troubles instead of looking from the parent changeset. All add a test checks that --rev works with several commits

evolve: extract cleanup logic in the evolve function We are going to need to reuse the cleanup logic when introducing --rev, so we extract it in a method to avoid code duplication.

evolve: simplify the evolve function We compute the troubles once and use it in two places instead of recomputing them just to count them.

evolve: optimize the computation of the troubled() revset We take the implementation from _counttroubles() and rely on the more efficient & operation for revset instead of laying down the entire set with %ld.

inhibit: don't inhibit pinned commits during rebase During a rebase we pin certain commits to always be visible. This caused the inhibit extension to inhibit them when a transaction closed. Let's make inhibit aware of such pins and not obsolete them.

evolve: extract the logic to solve one change into a method The goal is to later reuse this method to implement the --rev flag for evolve that solves the troubles in a revset.