* ENTITY INTERSECTS with the BOTTOM of the SLOPE.

From this, I learned: Be very careful with the distinction between the
SLOPE size and the OVERALL size.

* ENTITY gets STUCK trying to move DOWN the SLOPE.
* ENTITY INTERSECTS with the BOTTOM of the SLOPE.
fix: y1, y2 anchor conditions swapped.

* ENTITY cannot JUMP at the TOP of a SLOPE. (b>t)
y_overlap_amt is thrown off.
fix: y_lowering now takes SLOPE height into account instead of OVERALL
height.