--- a/mercurial/util.py	Fri May 21 15:22:29 2010 +0200
+++ b/mercurial/util.py	Fri May 21 19:54:40 2010 +0900
@@ -772,7 +772,7 @@
     file.  When rename is called, the copy is renamed to the original
     name, making the changes visible.
     """
-    def __init__(self, name, mode, createmode):
+    def __init__(self, name, mode='w+b', createmode=None):
         self.__name = name
         self._fp = None
         self.temp = mktempcopy(name, emptyok=('w' in mode),