[D-runtime] Chaining Errors

[Jonathan M Davis]

Throwable is chainable. Exception is chainable. Error is chainable. They all 
take an option Throwable argument in at least one of their constructors. 
Typically, all classes derived from Exception do the same. However, for some 
reason, none of the classes in core.exception which are derived from Error take 
a Throwable argument. Is there a particular reason for this? I'm inclined to add 
a default null Throwable to their constructors just like pretty much every other 
Throwable has. But I figured that I should enquire as to whether there was a good 
reason that I can't think of why none of the Error classes in core.exception 
take an optional Throwable.

- Jonathan M Davis