Added the quizzes_category_used() to detect the list of quizzes that are using questions from one category.
Added the quizzes_category_used() to detect the list of
quizzes that are using questions from one category.

It relies in the quizzes_question_used() function. Will
be use in the 'orphan_categories' bug (#2459)

(http://moodle.org/bugs/bug.php?op=show&bugid=2459)

Merged from MOODLE_15_STABLE

With some previously unmerged changes added too!! Please check them
Gustav!!

dilawar/moodle