The Jump class is a motion class which allows actors to jump.
Sets up the jump class.
Jumps the client actor towards the destination.
Sets the client's illegalBits and signal properties. If the caller is set, it sets the global variable gCastMotionCue to TRUE, and the completed property
Seperates the class from it's client (setting the client's mover to NULL). If the movement is complete and the caller is set, it cues the caller. Finally,
it disposes of itself.
Sets up the dx and dy properties.