another improvement for poor keyboard players

[joevenzon]

Okay, keyboard controls can now be set up to trigger when the key goes down or up. For the next VDrift release, disengage shift up is PAGEDOWN and disengage shift down is DELETE, like it is now. The difference is that PAGEDOWN and DELETE are also bound to engage (on key up). So when you want to shift up, you press PAGEDOWN which shifts the gear up and disengages the clutch, then when you release the PAGEDOWN key the clutch re-engages.