wininet: Add support for SSPI authentication for HTTP.

[Robert Shearman]

Juan Lang wrote:
> Hi Rob,
>
> +static UINT HTTP_DecodeBase64(LPCWSTR base64, LPSTR bin);
>  
> Do we really have to keep proliferating base64 implementations?  Could you
> not implement CryptStringToBinaryW instead?  Should be mostly a copy-paste
> job..
>   

CryptStringToBinaryW is a lot more complicated than just a base64 
encoder function, so this is beyond the scope of what I was trying to 
implement. I'll make a note to replace this code by CryptStringToBinaryW 
if someone does implement it though.

-- 
Rob Shearman