Backport the following changes: Misc/NEWS 1.387->1.388 Lib/test/string_tests.py 1.10->1.11, 1.12->1.14, Lib/test/test_unicode.py 1.50->1.51, 1.53->1.54, 1.55->1.56 Lib/test/test_string.py 1.15->1.16 Lib/string.py 1.61->1.63 Lib/test/test_userstring.py 1.5->1.6, 1.11, 1.12 Objects/stringobject.c 2.156->2.159 Objects/unicodeobject.c 2.137->2.139 Doc/lib/libstdtypes.tec 1.87->1.88 Add a method zfill to str, unicode and UserString and change Lib/string.py accordingly (see SF patch http://www.python.org/sf/536241) This also adds Guido's fix to test_userstring.py and the subinstance checks in test_string.py and test_unicode.py.

--- a/Lib/UserString.py	Mon Apr 22 11:21:59 2002 +0000
+++ b/Lib/UserString.py	Mon Apr 22 11:57:06 2002 +0000
@@ -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