dirstate: copyedit exception for no beginparentchange call

mercurial/dirstate.py

@@ -257,8 +257,8 b' class dirstate(object):'
         See localrepo.setparents()
         """
         if self._parentwriters == 0:
-            raise ValueError("cannot set dirstate parent without " +
-                " calling dirstate.begingparentchange")
+            raise ValueError("cannot set dirstate parent without "
+                             "calling dirstate.beginparentchange")
 
         self._dirty = self._dirtypl = True
         oldp2 = self._pl[1]