statwalk: don't put self.root in the files list

That list is supposed to contain internal, normalized names ("/"-separated,
relative to the repo root), not OS-native paths.

mercurial/dirstate.py

@@ -376,7 +376,7 b' class dirstate(object):'
 
         # walk all files by default
         if not files:
-            files = [self.root]
+            files = ['.']
             dc = self.map.copy()
         else:
             files = util.unique(files)