Make merror use surrounding font rather than MathJax fonts, and handle size of unknown text properly.
Make merror use surrounding font rather than MathJax fonts, and handle size of unknown text properly.

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