inhibit: use dirty revset trick to speedup the inhibit search space. See documentation for details. I'm a bit sad about this changesets.

inhibit: use 'repo.revs' instead of 'repo.set' This skip the creation of a changectx object.

_inhibitmarkers: turn the result from generator into a list A generator object is always True, we have to turn it into a list in order to be able to use it in the tests. Before this patch we were rewriting the 'obsinhibit' file all the time, this had a performance impact especially on repository where transaction are expensive (hooks, cache invalidation, etc). Writing this file less often have a minor effect on test where a stripped changeset does not get removed from the obsinhibit file is still inhibited when unbundled back. I think this is fine and I'm moving forward.