ExportOBJ

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   Export an OBJ file. This routine will create two files. One is
   fileName.obj  - geometry data
   fileName.mtl  - material data
   fileName.cad  - other than geometry data

   If you enter a fileName the extension will be ignored.
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   Form:
   ExportOBJ( g, fileName )
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   ------
   Inputs
   ------
   g           (:,:) CAD Data structure
   fileName    (1,:) Optional file name

   -------
   Outputs
   -------
   None

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