* NEWS: New option sort -C, proposed by XCU ERN 127, which looks

* NEWS: New option sort -C, proposed by XCU ERN 127, which looks
like it will be approved.  Also add --check=quiet, --check=silent
as long aliases, and --check=diagnose-first as an alias for -c.
* doc/coreutils.texi (sort invocation): Document this.
Also, mention that sort -c can take at most one file.
* src/sort.c: Implement this.
Include argmatch.h.
(usage): Document the change.
(CHECK_OPTION): New constant.
(long_options): --check now takes an optional argument, and is now
treated differently from 'c'.
(check_args, check_types): New constant arrays.
(check): New arg CHECKONLY, which suppresses diagnostic if -C.
(main): Parse the new options.
* tests/sort/Test.pm (02d, 02d, incompat5, incompat6):
New tests for -C.