nulldrv: Creation of the nulldrv, for use on Windows.

Since the sample Intel driver hasn't been ported to Windows, this nulldrv is
being used to bootstrap Windows support.  It can also provide a hint to new
IHV's for how to set the magic number.
diff --git a/.gitignore b/.gitignore
index 9389c83..cc557d2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,3 +20,4 @@
 layers/xgl_struct_string_helper.h
 layers/xgl_struct_wrappers.cpp
 layers/xgl_struct_wrappers.h
+_out64