revlog: get rid of defversion defversion was a property (later option) on the store opener, used to propagate the changelog revlog format to the other revlogs, so they would be created with the same format. This required that the changelog instance was created before any other revlog; an invariant that wasn't directly enforced (or documented) anywhere. We now use the revlogv1 requirement instead, which is transfered to the store opener options. If this option is missing, v0 revlogs are created.