manifest: rename manifestlog._treeinmem to ._treemanifests

Not sure what "inmem" was supposed to indicate. This object is an
interface to manifest data on disk as well as "in memory" (assuming
that's what "inmem" means).

Differential Revision: https://phab.mercurial-scm.org/D4278

mercurial/manifest.py

@@ -1418,7 +1418,8 b' class manifestlog(object):'
         if opts is not None:
             usetreemanifest = opts.get('treemanifest', usetreemanifest)
             cachesize = opts.get('manifestcachesize', cachesize)
-        self._treeinmem = usetreemanifest
+
+        self._treemanifests = usetreemanifest
 
         self._revlog = repo._constructmanifest()
         self._revlog._setupmanifestcachehooks(repo)
@@ -1466,7 +1467,7 b' class manifestlog(object):'
                 if node not in self._revlog.nodemap:
                     raise LookupError(node, self._revlog.indexfile,
                                       _('no node'))
-            if self._treeinmem:
+            if self._treemanifests:
                 m = treemanifestctx(self, '', node)
             else:
                 m = manifestctx(self, node)