manifest: set appropriate cache entry when clearing _dirlogcache() manifestrevlog applies to any manifest, not just the root manifest. Resetting the cache and populating its root entry with self is not correct when the instance does not refer to the root manifest. This has no test fallout. So I'm guessing we only ever call clearcaches() on the root manifest. Or we have no test coverage that are impacted by a bad cache on a non-root manifestrevlog. Differential Revision: https://phab.mercurial-scm.org/D4275

manifest: remove addgroup() from manifestlog and imanifestlog addgroup() is part of the storage interface for manifests. Unfortunately, we don't yet have a formal storage interface for manifests. (One will be established in subsequent commits.) One thing is for sure, addgroup() doesn't belong on imanifestlog - at least not unless we extend that interface to encompass storage. For now, let's access addgroup() on the _revlog attribute, just like we do for tree manifests. Even though this violates visibility, it is consistent. Differential Revision: https://phab.mercurial-scm.org/D4274