[amiwm] add a new command action to rotate windows

This adds a command to iterate over the set of windows.  It's not
like alt-tab in ye olde windows world where you'd alt tab once to
switch between two windows, and then keep alt-tab'ing with alt down
to go through the window list.  For now it just literally iterates
through those windows.

This makes it a lot easier to work with a large number of open
windows without having to constantly use the mouse.

module.h

@@ -14,6 +14,8 @@
 #define MCMD_GETICONDIR 16
 #define MCMD_GETICONPALETTE 17
 #define MCMD_MANAGEMENU 18
+#define MCMD_ROTATE_WINDOW_RAISE 19
+#define MCMD_ROTATE_WINDOW_LOWER 20
 
 struct mcmd_header {
   XID id;