perf: support measuring bdiff for all changeset related data The --all argument changes the behavior of `perfbdiff` to pull in fulltext revision pairs for all changes related to a changeset. The p1 and p2 manifests will be bdiffed against current. Every file that changed between p1 and current will have its file revisions loaded and bdiffed. This mode of operation effectively measured the bdiff time required for `hg commit`.