Fixed crash associated with .osg files which contain empty description fields.
From Sondra Inverson, added support to .ive plugin for osgSim::DOFTransform.
value to float, and converted the internal code across to use value_type. This
allows Matrix to be converted to use double's simply by change the definition
of value_type. Added Matrix::glLoadlMatrix and Matrix::glMultMatrix() to
help encapsulate the changes between float and double matrix usage.
Updated code that uses Matrix so it doesn't assume float or double matrices.
