Merge branch 'js/maint-1.6.1-filter-branch-submodule' into maint-1.6.1

* js/maint-1.6.1-filter-branch-submodule:
  filter-branch: do not consider diverging submodules a 'dirty worktree'

Author: gitster

git-filter-branch.sh

@@ -98,7 +98,7 @@ OPTIONS_SPEC=
 . git-sh-setup
 
 if [ "$(is_bare_repository)" = false ]; then
-	git diff-files --quiet &&
+	git diff-files --ignore-submodules --quiet &&
 	git diff-index --cached --quiet HEAD -- ||
 	die "Cannot rewrite branch(es) with a dirty working directory."
 fi