Cannot Check Exception Trait

[ajbeach]

Currently the exception handing mechanism uses an ad-hoc version of virtual types to implement its exception object. The type system does not know about these. The result of this is no assertion covers what the virtual type requires and the is_exception trait is empty.

Which means every type is an exception as far as the resolver is concerned. This is a problem that can't be solved right now. It requires the virtual system or equivalent to be implemented. But once it is this should be fixed, currently it crashes with a messy stack-trace.