Fixed header dependencies to be fully compatible with the Windows
headers (with help from Dimitrie O. Paun).

windows/user.c

diff --git a/windows/user.c b/windows/user.c
index d108aa4..f971f96 100644
--- a/windows/user.c
+++ b/windows/user.c
@@ -19,10 +19,12 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
+#include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
 #include "wine/winbase16.h"
 #include "windef.h"
+#include "winbase.h"
 #include "wingdi.h"
 #include "winuser.h"
 #include "wine/winuser16.h"