[dev-context] two patches

Hans, track-vis.mkiv has an future year. One of the enclosed patches fixes it. BTW, math-mkiv.pdf includes a \showglyphs commands that is used form where is needed to the end of the document. I guess this isn’t intended. I don’t know whether this is the best of way of doing it, but I enclose a patch to limit the \showglyphs command to the sample fonts in extensibles. Just in case it helps, Pablo -- http://www.ousia.tk