Inconsistent next_bb info when EXIT is a successor

[Andrey Belevantsev]

Steven Bosscher wrote:
 > I don't understand this.  You're saying there is a fallthrough edge
 > from your e->src to  EXIT_BLOCK. This case is explicitly allowed by
 > the checking code. It is an exception from the rule: For a fallthrough
 > edge to EXIT, e->src->next_bb != e->dest is OK.
Thanks!  It's the answer I was looking for -- this case is a known 
exception, so I shouldn't worry.  Given that ...

 > It is hard to tell without more context what your problem is. That
 > assert, is it an assert in your own code?  Maybe it is too strict?
... yes, the assert was too strict.  I've fixed that so we don't rely on 
next_bb in these cases.

Andrey