Pgeditor2bug

This includes a number of bugfixes, which I have tried to separate by commits.

1) I fixed a js error in the formchecker script for the Homework Sets Editor 2 page. You can test by trying to export something and looking for a javascript error. 
2) I fixed a bug where if a users wasn't assigned any homework it would cause past answers to not show any users listed later (when using regexp). Test by having a users with login "aaaaaaaastudent" not have any homework sets assigned to them and use regexps in Past answer.
3) I made it so that the achievement editor will not score dropped students. Test using a dropped student.
4) I made it so that the achievement editor provides a link where you can view the scoring file. Test obvious. 
5) I fixed a bug where the grader Mark Correct button did not undo itself if clicked twice. Test obvious. 
6) I fixed a bug in PGProblemEditor2 and PGProblemEditor3 where if you made a new version in a new window, opening views in a new window wouldn't actually use a new window.

7) I restored some old functionality to the PGProblemEditor2 where it used to dynamically check and uncheck the new window box depending on the selected option. Test by selecting different tabs and looking at the checkbox. 
8) Fixed a bug with export achievements where if you had selected all, sometimes nothing would be selected.