Fixed problem to be aware of with mathematical expression parts

[Christian Lawson-Perfect]

Hi everyone,

On March 31st I made a change to the 'rational' number type, to make it prefer converting to 'decimal' values instead of less-accurate 'number' values. This has had a few knock-on effects which caused weird-looking bugs.

I've just fixed what I hope is the last of these, affecting mathematical expression parts whose answers involve complex numbers where both real and imaginary parts are rational numbers, making them mark every answer incorrect.

I hadn't realised that the functions for checking equivalence of values produced by the student's answer and the correct answer didn't account for 'decimal' type values. They now do.

So, sorry about this. If you have any exam packages in use produced between March 31st and today, May 24th, please double-check them. And if you have any student attempts using such packages affected by this, and you're using the Numbas LTI tool, updating the package and re-marking should resolve it.

Christian