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/VertexProgram.cpp

@@ -171,7 +171,7 @@ void VertexProgram::apply(State& state) const
             ++itr)
         {
             glMatrixMode((*itr).first);
-            glLoadMatrixf((*itr).second.ptr());
+            (*itr).second.glLoadMatrix();
         }
         glMatrixMode(GL_MODELVIEW); // restore matrix mode
     }