Fix a bug such that if you enabled sorting by size (-S) and enabled a

Fix a bug such that if you enabled sorting by size (-S) and enabled a
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).