A task shouldn't become due before it is scheduled.

Based on my understanding of `scheduled` and `due` dates:

A task becomes due at `due - rc.due`. At that time it begins to be included in `+DUE` and to be displayed with `color.due`.

The earliest opportunity to work on a task can be scheduled later than `due - rc.due`. Doing this causes tasks to appear as "due" in reports and take on "due" urgency before any work on them can be done.

While these due-before-scheduled tasks can be hidden with `wait`, it's my opinion that preventing the condition would be a better solution.

Suggested change:

For any given task that is both `due` and `scheduled`, consider its `rc.due` to be `min(rc.due, due - scheduled)`.

If `rc.due` is recalculated for a task, use the recalculated `rc.due` when determining task color and whether to include a task in a report.

If `rc.due` is recalculated for a task, use the recalculated `rc.due` when pro-rating `urgency.due.coefficient` for the task. Tasks with smaller windows of opportunity should increase in urgency faster.