msglist: Refresh msglist recipient-header date text periodically to respond to current-date change #891
Description
Untested, but from reading code, it seems like if it's near midnight and you're looking at a recipient header that says "TODAY", it won't update to "YESTERDAY" after midnight unless something unrelated to the clock causes it to update. We can fix this by running a check every minute or so, to refresh the current-time value that controls that text.
(Same for the transition from "YESTERDAY" to an absolute date.)