Horizontal Parsons: blocks containing math do not render in PDF

[sean-fitzpatrick]

Thanks to some work by @geoff-cox , we can have math in a horizontal Parsons block.

However, conversion to LaTeX/print does not process the math.

For example, here is PTX source for hparsons with math:

      <exercise label="TaC-curvature-5" language="math">
            <statement>
              <p>
                Rearrange the blocks to form a valid identity.
              </p>
            </statement>
            <blocks layout="horizontal" randomize="yes" language="natural">
              <block order="8"><m>\unittangentprime(s)</m></block>
              <block order="7"><m>=</m></block>
              <block order="3"><m>\kappa</m></block>
              <block order="1"><m>\unitnormal(s)</m></block>
              <block order="2" correct="no"><m>\unittangentprime(t)</m></block>
              <block order="6" correct="no"><m>\gamma</m></block>
              <block order="4" correct="no"><m>\tau</m></block>
              <block order="9" correct="no"><m>\pi</m></block>
              <block order="5" correct="no"><m>\unitnormal(t)</m></block>
            </blocks>
      </exercise>

In PDF, this becomes: