`git status -u no` suppresses modified files too.

[Rusty Russell <rusty@rustcorp.com.au>]

This broke my "is this clean?" sanity check and very much violates
the man page description.

(I am now using `git diff --name-only` instead at Joel's suggestion.)

        $ git status
        On branch guilt/repro
        Changes not staged for commit:
          (use "git add <file>..." to update what will be committed)
          (use "git checkout -- <file>..." to discard changes in working directory)
        
        	modified:   tools/repro-build.sh
        
        Untracked files:
          (use "git add <file>..." to include in what will be committed)
        
        	.cache/
        	ANALYSIS
        	NOTES
        	SHA256SUMS
        	SHA256SUMS.asc
        	badpeer.json
        	base
        	channels.out.xz
        
        no changes added to commit (use "git add" and/or "git commit -a")
        $ git status -u no
        On branch guilt/repro
        nothing to commit, working tree clean
        $ git --version
        git version 2.19.1
        $

Cheers,
Rusty.