tmarshal patch for consideration

[Jeremy White]

On route to trying to fix the +heap warning, I actually
fixed it first by using the attached patch.

I believe this patch is correct; it makes any error in the
marshaling process sufficient to prevent an actual invocation.

However, it's a fairly fundamental behavior change, and I don't
know this code, so I thought I'd see if anyone objected before
I submitted it.

As far as I can tell, the behavior currently is that if we
can't demarshal a particular argument in a typelib, we go ahead
and call the function anyway.  This could conceivably have 
'good' side effects if the arguments we can't demarshall aren't used
by the caller.

The new behavior would be to fail anytime we don't understand
a parameter in the typelib.  That seems better to me, but again,
I'm really new to this code, so kibitzing appreciated.

Cheers,

Jeremy