manifest: add manifestlog.add

This adds a simple add() function to manifestlog. This lets us convert more
uses of repo.manifest to use repo.manifestlog, so we can further break our
dependency on the manifest class.

mercurial/localrepo.py

@@ -1732,7 +1732,7 b' class localrepository(object):'
                 drop = [f for f in removed if f in m]
                 for f in drop:
                     del m[f]
-                mn = self.manifest.add(m, trp, linkrev,
+                mn = self.manifestlog.add(m, trp, linkrev,
                                        p1.manifestnode(), p2.manifestnode(),
                                        added, drop)
                 files = changed + removed

mercurial/manifest.py

@@ -1049,6 +1049,9 b' class manifestlog(object):'
             self._mancache[node] = m
         return m
 
+    def add(self, m, transaction, link, p1, p2, added, removed):
+        return self._revlog.add(m, transaction, link, p1, p2, added, removed)
+
 class manifestctx(object):
     """A class representing a single revision of a manifest, including its
     contents, its parent revs, and its linkrev.