Made Matrix a typedef to Matrixf, and converted the old Matrix to Matrixf, as

part of prep for supporting both Matrixf (float) and Matrixd (double).

Added osg::Matrixf::glLoadMatrix() and osg::Matrixf::glMultiMatrix() methods
and changed corresponding usage of glLoad/MultMatrixf() calls across to use these
methods. Again prep for support Matrixd.

Fixes for VisualStudio 6.0 compile.

src/osg/ColorMatrix.cpp

@@ -32,7 +32,7 @@ void ColorMatrix::apply(State&) const
     if (s_ARB_imaging)
     {
         glMatrixMode( GL_COLOR );
-        glLoadMatrixf( _matrix.ptr() );
+        _matrix.glLoadMatrix();
         glMatrixMode( GL_MODELVIEW );
     }
 }