finalizing 64-bit mixed mode issues

[Vincent Povirk]

> 1. Loading 32-bit pure assemblies in 64-bit code. The patch you attached
> some time ago (which includes CorValidateImage implementation) works
> just fine for me. Do you have any plans for pushing it upstream soon?

I don't understand the ntdll parts. I just pulled those from Wine Staging.

The server probably needs to have special treatment for .NET images
rather than just skipping image format checks.

I can send the _CorValidateImage implementation, but it's not much use
without the rest of it.

I need to take more time to look into 2 and 3.