Log Message: 
Add a new context flag that controls how the student answer should be
displayed. The formatStudentAnswer flag can be set to 'evaluated'
(the default), which shows the final numeric answer; 'parsed', which
shows the fully parsed version (including extra parentheses for
clarity); or 'reduced', which performs constant operations, but
doesn't perform function evaluations or namedconstant substitutions.
For example, if the student answers 1+2+sqrt(3), then 'evaluated' will
produce 4.73205, 'reduced' will show 3+sqrt(3), and 'parsed' will
show 1+2+sqrt(3).
