Have Win DMD use gmake instead of a separate DMMake makefile?

[Walter Bright]

On the subject of friction, I believe we make a mistake by making a dependency 
on libcurl, a library over which we don't have control. Some issues:

http://d.puremagic.com/issues/show_bug.cgi?id=10710

http://d.puremagic.com/issues/show_bug.cgi?id=8756