Written in the D programming language

[Walter Bright]

These days, there are a number of web crawling spiders that go looking 
for source code to index. D source code tends to superficially look like 
C or C++, and someone who doesn't know D might misinterpret what it is.

I suggest that all D source code modules have the following comment at 
the top:

// Written in the D programming language.

This will help people who are googling for D source code, and will help 
people who don't know they're looking at D source.