bug#34490: console the user that his -n in sort --debug -n was seen

[積丹尼 Dan Jacobson]

Can you please have assure the user in that message it makes
that it has indeed seen his -n/--numeric-sort.

$ sort --debug
sort: using simple byte comparison
$ sort --debug --numeric-sort
sort: using simple byte comparison
                   ^^^^ unchanged. User gets nervous.

sort (GNU coreutils) 8.30. Sorry we discussed this before but kinda hard to 
find...