manifest: move treeinmem onto manifestlog

A previous patched moved all the serialization related options onto
manifestrevlog (since it is responsible for serialization). Let's move the
treeinmem option on manifestlog, since it is responsible for materialization
decisions. This reduces the number of dependencies manifestlog has on the old
manifest type as well, so we can eventually make them completely independent of
each other.

mercurial/manifest.py

@@ -957,6 +957,13 b' class manifestlog(object):'
     def __init__(self, opener, repo):
         self._repo = repo
 
+        usetreemanifest = False
+
+        opts = getattr(opener, 'options', None)
+        if opts is not None:
+            usetreemanifest = opts.get('treemanifest', usetreemanifest)
+        self._treeinmem = usetreemanifest
+
         # We'll separate this into it's own cache once oldmanifest is no longer
         # used
         self._mancache = repo.manifest._mancache
@@ -965,13 +972,6 b' class manifestlog(object):'
     def _revlog(self):
         return self._repo.manifest
 
-    @property
-    def _oldmanifest(self):
-        # _revlog is the same as _oldmanifest right now, but we eventually want
-        # to delete _oldmanifest while still allowing manifestlog to access the
-        # revlog specific apis.
-        return self._repo.manifest
-
     def __getitem__(self, node):
         """Retrieves the manifest instance for the given node. Throws a KeyError
         if not found.
@@ -984,7 +984,7 b' class manifestlog(object):'
                 isinstance(cachemf, treemanifestctx)):
                 return cachemf
 
-        if self._oldmanifest._treeinmem:
+        if self._treeinmem:
             m = treemanifestctx(self._revlog, '', node)
         else:
             m = manifestctx(self._revlog, node)