Fix relative date formatting to not split one day into two formats.

We were aware of this bug when we wrote the function, (that a date
six days in the past would be treated as the "Friday" or as the
"Oct. 23" case depending on whether its time was before or after
the current time today). We thought it wouldn't be a problem, but
in practice it is. In scanning search results with this output,
the transition between formats makes it look like a day boundary,
(so it would be easy to mistakenly think "Oct. 23" is Thursday).

Fix this to avoid confusion, (still being careful to never print
"Thursday" for a date 7 days in the past when today is Thursday).