Make LaTeX/PDF errors more visible

[teleological]

From rlpowell in #6:

It would be super nice to have the definition submission make a
micro latex file to test that you didn't screw up, and show the user errors as
necessary.

In the absence of fixing on a per-definition basis, the export should at least report the
LaTeX output to the user.  :P:P:P  But: The errors don't tell you where you are without
grepping teh latex.  -_-