- guiddef.h: Don't define GUID_NULL as extern as the official header set doesn't...

- guiddef.h: Don't define GUID_NULL as extern as the official header set doesn't do this. Also, it causes conflicts under some circumstances.
- regstr.h: Add missing _IN_KERNEL_ guard
- rpcndr.h: Don't use the DWORD type
- windef.h: Add missing types, and put some under the BASETYPES guard
- winnt.h: Don't define types which should be in windef.h
- winuser.h: Correct KEYBOARD_OVERRUN_MAKE_CODE declaration, add missing NOWINDOWSTATION guard
- ntgdityp.h: Fix header guard for "FIX" type declaration

svn path=/trunk/; revision=37721