run-test: add a test for json output when -i is used The -i can apparently confused some internal data structure, we want to make sure we do not regress.

changegroup: drop _changelog and _manifest properties We already have a _repo property on the packer, and we only access the changelog and manifest revlog in one place, so it's just as easy to get them from self._repo.

changegroup: document the cases where reordering complicates linkrevs

changegroup: extract condition for linkrev fastpath The condition for taking the fastpath (or not) is used in two places. By extracting it, we also provide a place to document what it's about.