CONTRIB-4760 :: N/A column report display is incorrect for Rate questions with N/A option selected

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
CONTRIB-4764 :: When deleting a question, number of existing responses to that question is sometimes wrong

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
Made code compliant with moodle coding guidelines (again!)

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>
2.5.7 (Build - 2013120200) ready for release.

Signed-off-by: Joseph Rézeau <moodle@rezeau.org>