Tail call elimination

[BCS]

Reply to bearophile,

> Walter Bright:
> 
>> I know how to do tail call optimization (it's a very old
>> optimization), but there are some technical problems with it in the
>> back end.

I read that as, "the DMD backend *can't* do tail call elimination" because, 
given how long Walter has been writing compilers, if it could, I'd be surprised 
if Walter wouldn't have added it yet. It may be a cases of "ya can't get 
that from here" or some such that would requiter a major rewrite for a relatively 
minor gain.