#42 InstructorGraded transactions cause class cast expcetions

[Robert D. Zeigler]

If an instructor assigns a score to a journal
assignment for a student (ie, from the gradebook; for
example, if the student sent their journal submission
by e-mail and the instructor wanted to give credit it
the e-mail submission), a class cast exception will be
thrown when the student attempts to submit future
journal entries for the same assignment (at the very
least, the CCE will occur if the
InstructorGradedAssignmentTransaction is the only
transaction for the particular assignment). The most
appropriate solution here isn't immediately obvious to
me... perhaps a subclass of journal assignment that is
also an InstructorGradedAssignmentTransaction (IGAT)?
Probably I will create an interface for IGAT, change
references to IGAT in the code to the new interface,
and let journal assignments implement the new
interface; then rework the code for gradebook additions
of scores for a particular assignment.