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.