Assignment 3 update.

I have updated the assignment 3 files.  If you're working on assignment 3, you
should delete all your *.class files and recompile the *.java files with the
updated jar file.

Also, the batch disk files *.dsk for each assignment are incompatible with
other assignments.  The batch disk files for earlier assignments won't work
with the current assignment.  Run your assignment against the batch disks
supplied with the assignment.