narrow: restrict manifest iteration by using manifest.walk(matcher) This is only for root nodes, so it shouldn't really matter (they're rarely huge), but seems cleaner. Differential Revision: https://phab.mercurial-scm.org/D2234

narrow: only diff manifest part within narrowspec when generating changegroup Since 959ebff3505a (manifest: add match argument to diff and filesnotin, 2017-03-07), we have a more efficient way of diffing manifests while applying a matcher. Let's use that while generating narrowed changegroups, so we avoid diffing parts of the manifest that don't match the narrowspec. Differential Revision: https://phab.mercurial-scm.org/D2233