Fix an issue with the graphtool default number line interval checker.

[drgrice1]

The checker for intervals compares the interval graphed by the student to the correct interval as MathObjects. However, the context of the graphtool is a modified Point context. This generally is fine. A half open or half closed interval or an unbounded interval is still an interval and the comparison works. However, a bounded open interval or a bounded closed interval both end up being points. As a result if the correct answer is a bounded open interval and the student graphs an interval with the same endpoints, but closed, the current checker counts that as correct.

To fix this, this sets the '[' paren to always be an interval the same as in the Interval context. The graphtool answers given by javascript will never need that to be anything else, so this works.

A minimal working example that demonstrates the issue is the following problem:

DOCUMENT();
loadMacros(qw{PGstandard.pl PGML.pl parserGraphTool.pl});

$graph = GraphTool("{interval, (1, 5)}")->with(
    availableTools => [ 'IntervalTool', 'IncludeExcludePointTool' ],
    numberLine     => 1
);

BEGIN_PGML
Graph the interval [`(1, 5)`].

[_]{$graph}
END_PGML

ENDDOCUMENT();

For the develop or main branch if you graph the closed interval from 1 to 5, it is counted correct. Of course, with this pull request it is incorrect.

Note that for all branches and this pull request the open interval from 1 to 5 is counted correct. Of course a half open (or half closed) interval from 1 to 5 and all other incorrect answers are counted incorrect.

You can also experiment with other correct answers, and they all should work with this pull request.

[pstaabp]

Fixes the issue.

[drgrice1]

@pstaabp is back!

[somiaj]

Confirmed this fixes the issue.