Fix dirstate fail at drive root on Windows

mercurial/dirstate.py

@@ -391,7 +391,7 b' class dirstate(object):'
 
         # self.root may end with a path separator when self.root == '/'
         common_prefix_len = len(self.root)
-        if not self.root.endswith('/'):
+        if not self.root.endswith(os.sep):
             common_prefix_len += 1
         # recursion free walker, faster than os.walk.
         def findfiles(s):