Fixed a couple of bugs

- Restored some of the responsive functionality of the "open in new window" checkbox that PG editor 1 had and was lost on the move to tabber (the old and the new)
- Changed it so that if you do save as in a new window, then using view in a new window from that window actually opens a new window.
Fixed bug with export achievements
fixed a bug where you couldn't undo a mark all correct on the problem grader page.
Scoring achievements provides a link to view the score file (since its pretty obscure)
Changed achievement scoring so that dropped and audit students aren't scored.
Fixed an issue where past answers behaved strangly when a user didn't have any defined sets.
Added some variable checking to a js file that was complaining about null values.
Made changes suggested in issue #273
Merge branch 'release/2.9' of https://github.com/openwebwork/webwork2 into pgeditor2bug
A small nitpicky change.  (What have I become!)

I made it so that the checkbox labeled input goes inside the label (like it should) and then had math4 add the checkbox class so the checkboxs are not offset from their labels.
Fixed a css bug with images in problems.
The previous image fix did fix things in IE but broke things in other browsers.  Added code to make the fix IE specific.
Third attempt at fixing ie problem. ...
Changed version
I made a couple of other tweaks to math4 to make it a little bit prettier.  In particular I made disabled or non open sets have a disabled button intead of text, and I used some css to make the buttons not drop below the check boxs/ radio buttons.
Merge pull request #324 from goehle/pgeditor2bug

Release 2.9 Bugfixing