[Halld-offline] changes related to CDC geometry

[Simon Taylor]

Hi.

I have just checked in several changes to the CDC geometry:
-- The sequence of angles of the stereo layers has been changed to 
conform to the engineering drawings (+--+ instead of -+-+)
-- The positions of the first wires in each layer at the center of the 
chamber and the stereo angles have been modified to conform to the 
positions of the holes in the end plates according to the engineering 
drawings.
-- The donuts and feed throughs have been added to the model
-- a thin aluminum mesh for supporting the FDC cables has been added to 
the volume just outside the CDC

I have also modified the following in the reconstruction code:
-- In the HDGEOMETRY library, code has been added to extract the 
parameters for the CDC geometry from the XML
-- In the CDC library, the code calls the geometry-extraction routine in 
DGeometry instead of using hard-coded numbers.

mcsmear has also been modified to get the geometry for both the FDC and 
the CDC from the XML.

Please let me know if you experience any issues related to these changes.

Simon