Merge branch 'ar/diff'

* ar/diff:
  Add tests for --quiet option of diff programs
  try-to-simplify-commit: use diff-tree --quiet machinery.
  revision.c: explain what tree_difference does
  Teach --quiet to diff backends.
  diff --quiet
  Remove unused diffcore_std_no_resolve
  Allow git-diff exit with codes similar to diff(1)

tree-diff.c

@@ -163,6 +163,8 @@ int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, stru
 	int baselen = strlen(base);
 
 	while (t1->size | t2->size) {
+		if (opt->quiet && opt->has_changes)
+			break;
 		if (opt->nr_paths && t1->size && !interesting(t1, base, baselen, opt)) {
 			update_tree_entry(t1);
 			continue;