Here's how it works: When a player walks off the
moving platform, it applies their pmomz once, and
then _keeps pmomz set_ so that the camera still
adds pmomz to its movements until they hit another
floor. This way, the camera doesn't jerk around.
Now players will apply platform movement when jumping,
but only if the platform is moving the same direction
as their jump is, and all other objects will have an
appropriate pmomz in reverse gravity FOF situations.