Support taller feet

Make the foot exterior cutout square as tall as FootHeight.
Previously making it taller than 100 made the top wider.
This is obviously ridiculous, but no harder to do right, and looks nicer
when debugging.

files/U_Box_V104_Test_Cleaned.scad

@@ -300,7 +300,7 @@ module foot(FootDia, FootHole, FootHeight) {
                 rotate_extrude($fn=100) {
                     translate([(FootDia + Filet*2) / 2, Filet, 0]) {
                          minkowski() {
-                             square(10);
+                             square(FootHeight);
                              circle(Filet, $fn=100);
                          }
                      }