GRIM: Joystick/gamepad support
GRIM: Fix keycode mapping of joystick 2 left movement.
GRIM: Change analog joystick position to discrete values.

This patch will map the analog joystick axis values to discrete values
(left/center/right). Without this the inventory in Grim Fandango behaves
erratic because every sample above the sensitivity threshold will be
mapped to a new button down event.