*\cROTATE_CONSTANT spawnflag

The crate func_train has the ROTATE_CONSTANT spawnflag set. Rotation speed for this
func_train is controlled solely by the path_corners (though you COULD also set the rotation
speeds for the train itself).

For ROTATE_CONSTANT func_trains, the pitch_, yaw_, and roll_speed values set at the
path_corners are the CHANGE in those values, not absolute quantities. This allows you to use
0's if you don't want a particular rotational velocity to change.

To turn OFF rotation in a given direction, set the _speed value at a path_corner to the
current value, but with the opposite sign.

The 1st path_corner sets the pitch_speed to 200, the 2nd path_corner uses -200 for
pitch_speed, which turns that rotation off, and sets yaw_speed to 200. The 2nd path_corner
has a short wait, and you'll notice that the func_train continues to rotate while 'waiting'.
The 3rd path_corner leaves yaw alone (yaw_speed = 0) and adds roll_speed = 200. Finally, the
4th path_corner (adjacent to the 1st) has both yaw_speed and roll_speed = -200, which sets
those values to 0.