Complete the diff generating functionality.

storage/local.py

@@ -38,6 +38,10 @@ class LocalStorage(Storage):
                     break
                 yield buf
 
+    def stream_read_file(self, path):
+        path = self._init_path(path)
+        return open(path, mode='rb')
+
     def stream_write(self, path, fp):
         # Size is mandatory
         path = self._init_path(path, create=True)