Added a Matrix::value_type typedef'd trait into osg::Matrix, defaulting its

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.

examples/osgshadowtexture/CreateShadowedScene.cpp

@@ -72,7 +72,7 @@ class CreateShadowTextureCullCallback : public osg::NodeCallback
                 virtual void apply(osg::State& state) const
                 {
                     glPushMatrix();
-                    glLoadMatrixf(_matrix.ptr());
+                    _matrix.glLoadMatrix();
                     TexGen::apply(state);
                     glPopMatrix();
                 }