revset: add larger test for heads(ancestors(…)) It is important to not regress on this benchmark so we move it into the "base" file. And we add another benchmark with more than two revisions.

revset-benchmark: use a generic revset to test `heads(commonancestors())` This allow to benchmark revset performance in other repositories than just the mercurial one.

revlog: reintroduce `revlog.descendant` as deprecated Reintroduce `revlog.descendant` to help extensions authors update their extensions in order to use the new API.

context: reintroduce `ctx.descendant` as deprecated Reintroduce `ctx.descendant` to help extensions authors update their extensions in order to use the new API.

obsolete: explode if metadata contains invalid UTF-8 sequence (API) The current metadata API can be a source of bugs since it forces callers to process encoding conversion by themselves. So let's make it reject bad data as a last ditch. I assume there's no metadata field which is supposed to store arbitrary BLOB like transplant_source.

obsolete: store user name and note in UTF-8 (issue5754) (BC) Before, user names were stored in local encoding and transferred across repositories, which made it impossible to restore non-ASCII user names on different platforms. This patch fixes new markers to be encoded in UTF-8 and decoded back to local encoding when displaying. Existing markers are unfixable so they may result in mojibake. I don't like the API that requires metadata dict to be UTF-8 encoded, which is a source of bugs, but there's no abstraction layer to process the encoding thingy efficiently. So we apply the same rule as extras dict to obsstore metadata.