[AD] D3D9 official SDK with MinGW

["Trent Gamblin" <trent@xxxxxxxxxx>]

I've "converted" (fixed un-typesafe stuff mainly) a few files:

wwindow.c
wsystem.c
wjoydxnu.c
directx_shader.c
prim_directx.c

To C++. Is this ok? The reasoning is all of these files now
use D3DX which barfs unless they're compiled as C++. This
allows anyone to use the official DirectX SDK with MinGW
instead of using a crippled one. The main advantage here is that
you don't have to use the d3dx9.dll that comes with these mingw
d3d distributions. Why is that important? Well, it's not legal to
distribute d3dx9.dll with a game unless it's part of a D3D redist.

So what I've done myself is have my installer include the redist
(you can choose to only package d3dx9 in the redist which makes
it just a couple megabytes). It works real slick, avoids any
potential legal problems (maybe unlikely but best to stay out of
those waters) and doesn't force the user on one specific version
of d3dx or make them include it beside their exe.

Just want to make sure this change is ok with everyone. I know
Allegro is a C library so there may be some opinions about this.
I think this is a positive change though, and it doesn't affect the
pure C interface of Allegro.

Trent