Use full location URL for xlink references in SVG <use> elements when the page includes a <base> element.  Resolves issue #831.
Use full location URL for xlink references in SVG <use> elements when the page includes a <base> element.  Resolves issue #831.

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