Apply the second version of SF patch http://www.python.org/sf/536241

Add a method zfill to str, unicode and UserString and change
Lib/string.py accordingly.

This activates the zfill version in unicodeobject.c that was
commented out and implements the same in stringobject.c. It also
adds the test for unicode support in Lib/string.py back in and
uses repr() instead() of str() (as it was before Lib/string.py 1.62)
diff --git a/Lib/UserString.py b/Lib/UserString.py
index f4f5cab..292e852 100755
--- a/Lib/UserString.py
+++ b/Lib/UserString.py
@@ -128,6 +128,7 @@
     def translate(self, *args):
         return self.__class__(self.data.translate(*args))
     def upper(self): return self.__class__(self.data.upper())
+    def zfill(self, width): return self.__class__(self.data.zfill(width))
 
 class MutableString(UserString):
     """mutable string objects