include: add initial winsta.h

[Austin English]

On Tue, May 26, 2015 at 10:21 PM, Austin English
<austinenglish at gmail.com> wrote:
> --
> -Austin

Patch has been pending for several days, is there something I can do
to improve it?

Nikolay asked in #winehackers where this came from, it's on MSDN:
https://msdn.microsoft.com/en-us/library/cc248871.aspx

and also in Process Hacker's source:
http://processhacker.sourceforge.net/doc/winsta_8h_source.html

-- 
-Austin