Add support for Number of takes

Here is a patch that is a first attempt at bringing the support for "number of takes" back into the module. It also adds in a check to see if the user has passed the quiz (originally posted in http://drupal.org/node/84816).

I have some questions about how we want to handle this, and I also wanted to post this for Deji, who said he had been doing some work in this section for a practice mode. Please review and let me know what you think.

My biggest question involves what should happen when someone has taken the quiz the full allotted number of times or has passed. It seems we might want to allow the option to retake the test (maybe in a kind of practice mode depending on your implementation Deji), retake the test and try to get a better score, or just show a results table where the student can go in and view the results of each attempt. Currently we are just responding true or false and settings an error or status message. Thoughts?

Note that this patch is based on http://drupal.org/node/88689 and created using an old and new directory, so you will want apply 88689, then apply this using:

patch -p1 < quiz_revisit.patch

Committed to HEAD. I figured that this fixes a major bug, and additional functionality (allowing them to take it anyway or showing the results, etc.) would be easy to add as an additional issue.