During a merge conflict, the name of a file may appear multiple
times in "git ls-files" output, once for each stage. If you use
both `--delete` and `--modify` at the same time, the output may
mention a deleted file twice.
When none of the '-t', '-u', or '-s' options is in use, these
duplicate entries do not add much value to the output.
Introduce a new '--deduplicate' option to suppress them.
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
[jc: extended doc and rewritten commit log]
Signed-off-by: Junio C Hamano <gitster@pobox.com>
