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.

include/osg/State

@@ -100,7 +100,7 @@ class SG_EXPORT State : public Referenced
                 if (matrix) 
                 {
                     _projection=matrix;
-                    glLoadMatrixf(matrix->ptr());
+                    matrix->glLoadMatrix();
                 }
                 else
                 {
@@ -123,7 +123,7 @@ class SG_EXPORT State : public Referenced
                 if (matrix)
                 {
                     _modelView=matrix;
-                    glLoadMatrixf(matrix->ptr());
+                    matrix->glLoadMatrix();
                 }
                 else 
                 {