MathQuill doesn't get along with text entry answers that involve function names

[dlglin]

This was motivated by OpenProblemLibrary/272/setStewart14_7/problem_9.pg. I have submitted #967 to fix that particular problem, but I'm opening this report in case there are other OPL problems which this affects.

The referenced problem contains an answer blank with the answer checker ANS(str_cmp("local maximum"));. If a student types the word maximum, MathQuill adds a space after "max" since max is a known function, so the answer submitted is "local max imum", which is marked wrong. Students can get around this if they know to use text mode in MQ, but this isn't mentioned in the instructions in the question (and possibly shouldn't be in case MQ isn't enabled). @Alex-Jordan mentioned a similar issue in openwebwork/webwork2#1804 with "Prime" and the Pr function.

In most of these types of cases I think the right thing to do is to replace text entry with fixed response (radio buttons or popup menus), but I haven't tried to track down all of the problems that this affects.

[Alex-Jordan]

My proposal is that we cut the list of MQ operators way down to just the trig and logarithm functions. Would there ever be a case where it is beneficial to a student typing an answer to have max be recognized as an operator? Or if so, wouldn't it be so rare among WW exercises that it would be OK to not give it special formatting?