phases: extract the intermediate set of affected revs When advancing phases, we compute the new roots for the phases above. During this process, we need to compute all the revisions that change phases (to the new target phases). Extract these revisions into a separate variable. This will be useful to record the phase changes in the transaction.

phase: put retractboundary out of the loop in advanceboundary It seems that we were calling retractboundary for each phases to process. Putting the retractboundary out of the loop reduce the number of calls, helping tracking the phases changes.