- solidify/overlap.c (rotate): don't reverse y shift either
- solidify/overlap.c (scroll_event): reverse rotation (since we've fixed
the math of the coordinate transformation)
- solidify/overlap.c (scroll_event): reverse rotation if mouse is on the
left side
- solidify/overlap.c (shift): reversing the direction in the "down"
quadrant is systematic but quite confusing, so don't do it