make x11 keyboard repeat detectable

By default, x11 inserts KeyRelease events for every repeated KeyPress event when you hold a key down. This makes it impossible to detect that the key is still being held down and repeated vs tapped quickly. Not so useful for game dev where you what to do something while a key is being held. This changes the behavior to repeat KeyDown events on repeat without interleaving KeyRelease events. I don't know what the behavior is on other platforms, does this need to be user-configurable?

(see http://linux.die.net/man/3/xkbsetdetectableautorepeat)