Finally fixed the flap drag issue. Drag modifications need to be based on

Finally fixed the flap drag issue.  Drag modifications need to be based on
the amount of drag that the produced lift *would* have produced given an
unflapped air surface.  A nifty trick involving the assumption that AoA is
small works for this, and produces plausible results in the high AoA case
as well.

Also, trim for approach using the elevator-trim control, not elevator.
Just cosmetic for current planes, but future ones might have differing
implementations of trim.