Merge branch 'mt/patch-id-stable' (early part)

* 'mt/patch-id-stable' (early part):
  patch-id-test: test stable and unstable behaviour
  patch-id: make it stable against hunk reordering
  test doc: test_write_lines does not split its arguments
  test: add test_write_lines helper

t/test-lib-functions.sh

@@ -717,6 +717,11 @@ test_ln_s_add () {
 	fi
 }
 
+# This function writes out its parameters, one per line
+test_write_lines () {
+	printf "%s\n" "$@"
+}
+
 perl () {
 	command "$PERL_PATH" "$@"
 }