transaction: build changes['revs'] as range instead of a set Revisions are added consecutively, so a range can easily represent them in the changes list. This saves around 45 Bytes / revision on 64bit platforms and reduces the memory footprint of issue5691 by 15MB. Don't copy changes['revs'] in getobsoleted. Ranges have a very efficient contains implementation already. Differential Revision: https://phab.mercurial-scm.org/D1615