[dmd-concurrency] Thread termination protocol (shutdown protocol evolved)

[Andrei Alexandrescu]

Michel Fortin wrote:
> I disagree about inheriting from Error: Terminate isn't an error. You're probably right that it shouldn't be an Exception, so in that case it should inherit from Throwable, not Error.

The hierarchy as described in TDPL has Error and Exception inheriting 
Error. I think it's ok to rename Error into the more descriptive 
Throwable. Sean?

Andrei