Changes

## "[Upon unlock() t]he system mouse cursor must be displayed again and positioned at the same location that it was when mouse lock was entered (the same location that is reported in screenX/Y when the mouse is locked)"

## "When mouse lock is lost or disabled for any reason user agents must fire an event named mouselocklost with its bubble attribute set to true to the mouse lock target element"

## "The members movementX and movementY must provide the change in position of the mouse, as if the values of screenX/Y were stored between two subsequent mousemove events eNow and ePrevious and the difference taken movementX = eNow.screenX-ePrevious.screenX"

## "movementX/Y must be valid regardless of mouse lock state"