Merge branch 'jc/clean' into next

* jc/clean:
Teach git-clean optional <paths>... parameters.
Separate object name errors from usage errors
Documentation: {caret} fixes (git-rev-list.txt)
Fix "git diff --stat" with long filenames
Fix repo-config set-multivar error return path.

diff --cc diff.c
Simple merge

diff --cc read-tree.c
Simple merge