treemanifest: fix a "treeinmem" case f2c5b9d48b29 (manifest: make treemanifestctx store the repo, 2016-10-18) broke most tests when run with treeinmem=True. The treeinmem mode can not be enabled by the user, so this did not break anything in practice, but it's useful to have it working for testing the treemanifest code.

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`.

perf: support bdiffing multiple revisions in a single revlog This is useful for testing bdiff performance on several revision pairs at a time.

perf: prepare to handle multiple pairs in perfbdiff Before, we only supported benchmarking a single pair of texts with bdiff. We want to enable feeding larger corpora into this benchmark. So rewrite the code to support that.