Convert mod/quiz/view.php to roles, and further tidy up the code flow in there. This...

Convert mod/quiz/view.php to roles, and further tidy up the code flow in there. This touches other files because I had to change a function in locallib that had an $isteacher parameter.

I have not converted the rest of the quiz, and I don't intend to. I am hoping Moodle.com will do it.

I hope this does not introduce any bugs, but view.php is so complicate (at least it is less complicated than it was) and the quiz has so many options, that it is hard to be sure. This needs lots of testing before 1.7 is released.