Correct lighting for back faces with shaders

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33055 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
change variable name 'l'

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33057 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Correct lighting for back faces with shaders (web)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33060 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Correct lighting for back faces with shaders (web)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@33061 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e