Fix breakage f87a0b caused with gl_Normal

.. "Never use built-in attribute names on OpenGL ES"
had a bad interaction with the special-case code of:
"
if (sem == EAttrSemNormal && size == 4)
	pad = 1;
"
.. so I improved this such that it now specifically
targets the usage of "gl_Normal".

The testcase that failed was z-ogre-grass2-outES.txt