[winedbg] Don't ever pass a NONCONTINUABLE exception

[Glenn Wurster]

> > Changelog:
> >    Don't pass on non-continuable exceptions.
> 
> Why do you want to do that?

In short, because we're never going to be able to continue, so there's
no point on trying to pass because that's going to fail.

In long, because I've got another patch in the pipeline (it needs some
tweaking) that moves the calling of the debugger into the signal
handler.  It allows the debugger to catch exceptions that would
previously have resulted in a total crash (non-continuable
exceptions), and it more accurately reflects how the Windows debugger
is called.  Using a debugger will also no longer modify program memory
as it does currently.  In all, it should allow the debugger to work in
more circumstances than it currently does.

Glenn