Split the 'error.py' file into two, one for the RelaxErrors and the other for the RelaxWarnings.
This change was mentioned at https://mail.gna.org/public/relax-devel/2007-02/msg00009.html
(Message-id: <7f080ed10702260432v3201e4f8o473e6e6c27eefb1a@...>).