Contribution page start/end dates don't affect widget's total contributions sum

When using a contribution widget associated with a particular contribution-page, it would be nice to be able to modify the start/end dates of the contribution page, and have them affect which contributions are included when computing the sum that is displayed by the widget. Currently this date-range has no effect on the computed widget sum.

The use-case is this: a contribution page is set up, and the user wants to continue to be able to use the same contribution page and widget, but to adjust the date-range (e.g. to match a new year or matching-grant period) on occasion.

On a tangentially related topic, it would probably be better to still allow people to access a contribution page even if the current date is outside the start/end date range. Otherwise potential donors are greeted with an "invalid page" message instead of a form by which they can donate.