Expression switch exception naming

[Brian Goetz]

> NoCaseMatchError (or any other name) which is a subtype of IncompatibleClassChangeError.

I buy the "subtype of ICCE" argument, but it seems to me these need to 
be exceptions, not errors.  (Thought experiment: if we already had both 
ICC{Exception,Error}, would we have jumped so fast to Error?  I don't 
think so.)  I'd support adding ICEException and having these be subtypes.

Adding a new enum value is not the same sort of obviously-incompatible 
change as changing a static method to instance, or a concrete method to 
abstract, which are the sorts of things that trigger ICCError.

On the naming front, I would think this is more in the category of 
"unexpected class change exception" than "incompatible change." Adding a 
new enum constant isn't intrinsically evil.  If anything, the issue is 
on the client, who relied on the assumption of of exhaustiveness.