C++ exceptions

[Kasper Peeters <t16@nikhef.nl>]

Today, I worked a full hour to find a trivial bug in the OIL loading
procedure. Since this would have been avoided with proper error
reports, I decided to start using C++ exceptions instead of having
random 'cerr' or 'debug' statements. This will also make it easier
to report errors to the user.

This has the side effect that you will now need a decent C++ compiler,
but I think it's worth it. EGCS is fine.

Back to the filter stuff now...

Kasper