Don't let svg element be focusable in IE.

unpacked/jax/output/SVG/jax.js

@@ -2103,6 +2103,7 @@
           if (alttext && !svg.element.getAttribute("aria-label")) span.setAttribute("aria-label",alttext);
           if (!svg.element.getAttribute("role")) span.setAttribute("role","math");
 //        span.setAttribute("tabindex",0);  // causes focus outline, so disable for now
+          svg.element.setAttribute("focusable","false");
           span.appendChild(svg.element);
           svg.element = null;
           //