run-tests: obtain code coverage via Python API Before, we were invoking the "coverage" program provided by the "coverage" module. This patch changes the code to go through the Python API. This makes the next patch a little bit easier to reason about. A side effect of this patch is that writing code coverage reports will be slightly faster, as we won't have to redundantly load coverage data.

commands.debugrevlog: report max chain length This is sometimes useful to know. Report it.

_lazymanifest: drop unnecessary call to sorted() The entries returned from _lazymanifest.iterentries() are already sorted.