Patch for better diagnostic (was: Re: Bug in MI?)

[Jason Merrill]

>>>>> Manfred Hollstein <manfred@s-direktnet.de> writes:

>> That can't be right; you can't treat error_mark_node like a TREE_LIST.

> Perhaps, you're wright. But that treatment isn't new due to my patch. I only
> added the the different error message, the while loop was already there.

Agreed.  The old code didn't recognize that we could get an error_mark_node
there.  Do you mind fixing it?

Jason