KFormat::formatRelativeDate allows one to obtain a human-readable date like "Last Wednesday" or "Next Thursday" for dates within a week of the current date.

The returned string cannot be properly translated in all languages since it's generated using a placeholder of the form "Next %1" -- the word Next (or Last) may itself need to be modified to be correct which can't be done with the current translation system.

The fix is just to return "Next $dayName" directly, based on the day name as appropriate, and allow the translators to translate the entire phrase.

The auto tests are adjusted as well. They were actually incorrect before this change, since the API documentation for formatRelativeDate makes clear that the date format is only applied if the date is *not* within a week of the current date.

See also Bug 335106.

Change builds and installs properly, and all kcoreaddons tests continue to pass (with the kformattest autotest revised per this change).