ui-shared: show full date in tooltip if longer ago than max_relative

Commit caed6cb (ui-shared: show absolute time in tooltip for relative
dates, 2014-12-20) added a toolip when we show a relative time.

However, in some cases we show a short date (that is, the date but not
the time) if an event was sufficiently far in the past and that commit
did not update that case to add the same tooltip.

Signed-off-by: John Keeping <john@keeping.me.uk>