discovery: filter null from the discovery revset If there is nothing in common, common will be "null" and the revset will now returns "-1" crashing the discovery process. We filter out the null revision to prevent that.

tests: update to new core output Multiple output change need to be applied to the test suite.

evolve: explicitly disable bookmark on evolve (issue4432) We no longer leave the current bookmark active after an evolve, since it is no longer pointing to the working directory.