Prevent reverse bug near screen edges
Remove control of RocketSkateboard
Ignore eggbeaters while on skateboards.

Erik made his levels with the thought of skateboards not changing
directions. So I suppose either the scientist should get off the
skateboard or ignore eggbeaters.
Fixes #31

"If the skateboard has the scientist on it and the two interact with the
JackInTheBox and the scientist cannot perform the super bounce up the
floor, the skateboard goes crazy."
Remove unnecessary line.
Fix reversing bug while near a wall.
Get off Skateboard after Eggbeater encounter.

I'd prefer to do this another way...