Remove spacing from under and over scripts (see issue 815), and handle the bbox.D value better when there are multiple elements in an mrow.
Remove spacing from under and over scripts (see issue 815), and handle the bbox.D value better when there are multiple elements in an mrow.

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