Patch for 0.7.4

t figures that just after 0.7.4 is released, I discover yet another bug in the program. The program does not properly handle comments for dropped students. While GradeL does not crash, comment data for dropped students is not saved and therefore lost upon closing the program. Grade information is not lost. I'll post a patch to file GClass.class on the website http://gradel.sourceforge.net.