- Page up/down changes the selected throttles one step up/down, i.e.
if the original throttle settings were x steps apart they remain
steps apart (unless the boundary is reached).
- Mouse + MMB drag changes the selected throttles by the delta amount
(length of drag).
- The throttleAxis() wrapper for joysticks sets the selected
throttles to correspond to the joystick's axis position. I.e. all
selected engines will get the same throttle setting. Since most
joystick throttles are positional devices I think this behaviour
is more logical than using a relative adjustment in this case. """
mf: slightly modified, added var etc. (more such changes in controls.nas
to come)