compiler support added for precise GC

[Andrei Alexandrescu]

On 4/16/12 1:31 PM, Alex Rønne Petersen wrote:
> I think we can safely settle on bitmaps for this. Most real world GCs
> use this kind of strategy.

This is a valid argument, but I should say it's very much worth 
exploring techniques enabled by D specifically. Many unique and superior 
D idioms would not have existed if we played it safe and did things like 
everybody else did.

Andrei