There was a clipping bug where the player could sometimes clip thru a
left-side wall, if the left wall and floor made a 90 degree bend and the
player was holding the Left key while jumping slightly into the wall.
A band-aid that seems to work involved two steps:
1. When capping their leftward movement, add a "+ 1" to the cap.
2. At the start of the point loop, enforce the left cap like we do the
ceiling cap.
This seems to patch the problem, BUT it breaks the ability to walk up
slopes while moving left. Right-facing slopes can be climbed fine still.
Note: the original bug never was a problem against right walls, only
left ones, but the true root cause was not identified. See TODO comments
in collide_level.go.
Noah Petherbridge
695ff4da42