Q2Mat:

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   Converts a quaternion to a transformation matrix.
   Does not check to see that m is orthonormal.
   This routine requires 45 floating point operations.

   Since version 1.
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   Form:
   m = Q2Mat( q )	
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   ------
   Inputs
   ------
   q		(4,1)  Equivalent quaternion

   -------
   Outputs
   -------
   m		(3,3)  Orthonormal transformation matrix

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	References: Shepperd, S. W., Quaternion from Rotation Matrix,
               J. Guidance, Vol. 1, No. 3, May-June, 1978, pp. 223-224.
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