Remove quick fix for overwrite bug

Somehow the overwrite bug has disappeared!
Consequently, the quick fix isn't needed.
Introduce clearing the input queue

Before, holding down the movement keys
made the game go turbo. The simple solution
to this would, instead, lock up the game for
a few seconds when you held any button for
too long.
Implementing the simple solution and then
clearing the input queue each time we get
input solves both problems.
Finish fix-speedup
Merge pull request #3 from MageJohn/develop

Develop