Slate Windows build

[Todd Fleming]

Shaping wrote:

> windows-extprim.c, extprim.c, boot.c, ansifile.c include "slatevm.h", 
> which doesn't exist.  I changed this reference to "vm.h".

I think this is intentional. Copy whatever vm you are working on to 
slatevm.*.

>
> Project windows now compiles and links with 99 warning, most of which 
> are type-cast-related.  Perhaps we should cleanup some of these.  
> Suggestions?

I have this in my local copy:
#pragma warning(disable: 4214 4200 4100 4054 4057 4146)

Todd