<_description>
Repeatedly rotates a bitmap by 90 degrees by using logical operations:
the bitmap is divided into quadrants, and the quadrants are shifted
clockwise. Then the same thing is done again with progressively
smaller quadrants, except that all sub-quadrants of a given size are
rotated in parallel. As you watch it, the image appears to dissolve
into static and then reconstitute itself, but rotated.
Written by Jamie Zawinski; 1992.