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   Propagates a quaternion one step assuming that the angular velocity
   is constant. 
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   Form:
   q = AttProp( w, q, dT )
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   ------
   Inputs
   ------
   w            (3,1)     Angular velocity
   q            (4,1)     Old quaternion
   dT           (1,1)     Time change

   -------
   Outputs
   -------
   q            (4,1)     Updated quaterion

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