Thanks for the patch!

It looks pretty good, but there is one problem I see.  There should be a test_main() function for this to work from regrtest.  For example, take a look in Lib/test/test_bool.py.  Also, I don't think you need to seek(0) before getting the value from sys.stdout (ie, cStringIO instance).

I don't think you need to support sys.platform == 'mac'.  That was for Mac OS 9 which is no longer supported (see PEP 11).  Mac OS 10 has sys.platform == 'darwin'.  If you're interested, it would be good to produce a patch to remove all (10+) occurrences of comparing sys.platform with mac.

I'm assigning this to Ronald just so he can verify the Mac OS 9 issue.  Ronald, please comment and then unassign or assign to me.