Py2.4 delta test and CredentialsIter fix

Here is my delta test adapted for Python 2.4.

I also threw in a change I made for the earlier version of the Python 3 port that allows Python 2.6’s next() built-in function to be called on _ra.CredentialsIter objects.

Both of these changes are for Python 2 only and should be left out of the Python 3 branch.