Test that delta.apply_txdelta_window() and friends work

Patch from Martin Panter.

Signed-off-by: Jelmer Vernooij <jelmer@samba.org>
Make _ra.CredentialsIter a proper iterator in Python < 3

This allows Python 2.6’s next() built-in function to be used. Previously
only calling the next() method would work.

Patch from Martin Panter.

Signed-off-by: Jelmer Vernooij <jelmer@samba.org>