[2/6] winhttp: Allow winhttp to use wininet.h with winhttp.h

[Dan Kegel]

James wrote:
> I thought the idea was to implement winhttp and then
> implement wininet on top of winhttp.  Why are you importing wininet?

As of January, Hans was still talking about implementing
winhttp on top of wininet
( http://www.winehq.org/pipermail/wine-devel/2008-January/062172.html
http://www.winehq.org/pipermail/wine-devel/2007-August/058420.html )

It's not clear one can fully implement either wininet on top
of winhttp or vice versa.  We will probably need some code
duplication or private interfaces eventually.

Building winhttp on top of wininet lets us develop on trunk and
is probably the fastest path to making a bunch of applications
happy, isn't it?   That's the way I'm leaning, anyway.
- Dan