flag to use a time other than modtime (-c, -u, or -U), the output would
actually be sorted by the specified time rather than size. This does
alter the behavior in the case where both -S and -t are specified. Now,
-S is always preferred. Previously, -t was preferred if one of -c, -u, or
-U was specified, and -S was preferred otherwise. Perhaps -S and -t should
override each other (last one specified wins).