[D-runtime] Why does druntime us .di files instead of .d?

[Jonathan M Davis]

On 2011-07-13 13:36, Walter Bright wrote:
> .di files are used when they are generated from .d files.

Yes. I get that. But why are .di files generated in the first place? Phobos 
just uses .d files. It doesn't generate any .di files. druntime, on the other 
hand, generates .di files, and that's what you end up importing when you 
import core.*. I don't understand why the .di files are being used at all.

- Jonathan M Davis