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.
glMatrixMode( GL_MODELVIEW ); after the setting of the texture matrix.
Previously the texture matrix mode could run into normal model view
matrix operations which were assuming the defaul of GL_MODELVIEW.
