Unwind API for EH

[Cary Coutant]

>I think the idea was more to generalize the interface: there are N values
>that you want to communicate to the landing pad.  It doesn't matter which
>registers you use to pass these.  For a register-poor architecture like the
>ia32, you might even combine the values into a struct and use only a single
>register.  Cary's suggestion allows us to leave this decision up to the
>unwinder library, so the personality routine can be more general.

Thanks, Jason. I've been meaning to respond, but your response states my 
rationale quite eloquently.

-cary