add failing unit tests from wiki and try-ctop page
make bind better

Now matches http://www.w3.org/Math/testsuite/build/main/Content/ArithmeticAlgebraLogic/logic7-form.xhtml sample rendering
cope with deprecated <fn> tag

just transform its contents
use the right char for <approx>
bracket <not> correctly

(I think)
<divide> always produces an <mfrac>

instead of an <mrow> with a / character in the middle