Since we can't predict how many valuators may be in a future SD attached to an
MD, we need to preallocate a history buffer that is large enough to keep
MAX_VALUATORS coordinates per event.
In addition, the history buffer needs to memorize the coordinate ranges at the
time, thus requiring MDs to store (min_val, max_val, current_val, time)
instead of (current_val, time) for each motion history entry.
This commit only fixes the allocation.
d22c25bda4