Jack Jansen reported that the regression test failed on the Mac where

string.letters was much more than expected.

Solution: explicit is better than implicit; don't rely on
string.letters.

Lib/test/test_StringIO.py

 # Tests StringIO and cStringIO
 
-import string
-
 def do_test(module):
-    s = (string.letters+'\n')*5
+    s = ("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"+'\n')*5
     f = module.StringIO(s)
     print f.read(10)
     print f.readline()