exchange: improve computation of relevant markers for large repos Find the candidates for nodes with relevant markers by going over all markers instead of iterating over all nodes. Most nodes will not have markers anyway. Further optimize the code by allowing revsets as well, which reduces the materialization cost.

branching: merge stable into default

narrow: add a test for linkrev computation done during widen This new tests show that the linkrev computed and sent by the server might end up being wrong during a widen operation.