Add support for \{, \} and \\ inside \text{}, since {, }, and \ are used by MathJax in determining the extent of the \text box.  This helps with issues #375 and #790.
Add support for \{, \} and \\ inside \text{}, since {, }, and \ are used by MathJax in determining the extent of the \text box.  This helps with issues #375 and #790.

anueshenxing/MathJax,Edraak/MathJax,jeremykenedy/MathJax,nvp2211/MathJax,anusornc/MathJax,mcanthony/MathJax,GerHobbelt/MathJax,mcanthony/MathJax,perseoq/MathJax,jinntrance/mathjax,perseoq/MathJax,physikerwelt/MathJax,minrk/components-mathjax,thomasjm/MathJax,jinntrance/mathjax,cheerfulstoic/MathJax,anusornc/MathJax,minrk/mathjax-component,ManrajGrover/MathJax,wikimedia/MathJax,cheerfulstoic/MathJax,minrk/components-mathjax,anueshenxing/MathJax,cben/MathJax,thomasjm/MathJax,minrk/mathjax-component,jeremykenedy/MathJax,Ivanwangcy/MathJax,cben/MathJax,ManrajGrover/MathJax,Ivanwangcy/MathJax,rachetfoot/MathJax,thomasjm/MathJax,GerHobbelt/MathJax,Edraak/MathJax,thomasjm/MathJax,thomasjm/MathJax,nvp2211/MathJax,dpvc/MathJax