Handle msup and msub children properly.
Handle msup and msub children properly.

dpvc/MathJax,wikimedia/MathJax,thomasjm/MathJax,thomasjm/MathJax,jinntrance/mathjax,thomasjm/MathJax,thomasjm/MathJax,GerHobbelt/MathJax,thomasjm/MathJax,jinntrance/mathjax,GerHobbelt/MathJax