Removed a lot of occurences of windows.h (and added necessary other
includes).

diff --git a/misc/tweak.c b/misc/tweak.c
index 9ce44e0..69a63d6 100644
--- a/misc/tweak.c
+++ b/misc/tweak.c
@@ -29,7 +29,7 @@
  *****************************************************************************/
 
 #include <string.h>
-#include "windows.h"
+#include "winuser.h"
 #include "tweak.h"
 #include "options.h"
 #include "debug.h"