When a user begins a quiz but will not be able to use the full time limit to complete the quiz before the quiz closes, the user should be warned of this before they begin the attempt. Currently, it is not absolutely clear to the user on the quiz page that the close date takes precedence over the time limit.  As such, it's easy to assume the close date just means the last time an attempt can begin.  When a quiz is in the "closing window" timeframe (i.e., with less time before the quiz closes than is allotted in the time limit), the user should see two things:

1. mod/quiz/view.php should change "This quiz will close at" to "All attempts must be submitted by"  AND a warning label should appear immediately below the "Time limit" line to say "Warning: quiz close date will occur before time limit"
2. In the popover that displays to remind the user of the time limit, a stark warning should appear at the end of the message to say "Warning: you have less than the allotted $time_limit to submit this attempt."