SAM-2157 calculated question - added test cases to confirm that formulas work as expected and also improved the NaN and Infinity error messages

git-svn-id: https://source.sakaiproject.org/svn/sam/trunk@124673 66ffb92e-73f9-0310-93c1-f5514f145a0a
SAM-2157 calculated question - improved user error messages

git-svn-id: https://source.sakaiproject.org/svn/sam/trunk@124674 66ffb92e-73f9-0310-93c1-f5514f145a0a