gdiplus: implement GdipTransformPoints

[Nikolay Sivov]

Vincent Povirk wrote:
> It's odd, but it seems like the simplest way to write this.
>
> I've tried what I think was your suggestion, and that's attached. I
> don't think it's an improvement.
>
> Vincent Povirk
>
>   
Could be a single switch maybe. Don't know, looks better for me.
Comparisons were really ugly here - a strict comparison should be used 
instead if you don't like
switches.

Anyway it's just my thoughts.