Issue #2299233: Fixed Multiple choice question type can be skipped even when "allow skipping" is disabled.

Fixed issues when a user with "administer nodes" or some other permission that is not explicitly "create quiz content" is not granted the ability to edit scale collections or browse for question terms. Use node_access instead.

Issue #2278083: fixed randomized questions not building index correctly. renumber the array so things like quiz_is_last_question work.

Fixed several issues with quiz_get_questions() returning duplicate questions. This did not have much effect on quiz taking because the list was unique-ified.

Fixed tests that were actually wrong.

Fixed a couple of notices in Scale.

Changed the unix date fields time_start and time_end to NULL so that the year 1969 cannot be stored. We also get better views filtering with this (time not empty, etc.)

Added test for testQuestionRepeatUntilCorrect().