convert: update the transplant, rebase and graft references in 'extra' This change allows the origin() and destination() revsets to yield the same results in the new and old repos after a conversion. Previously, nothing would be listed for queries in the new repo. Like the SHA1 updates to the commit messages, this is only operational when the 'convert.hg.saverev=True' option is specified. If the old reference cannot be found, it is left as-is. It seems slightly better to leave stale evidence of the graft/transplant/rebase than to eliminate it entirely.