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

diff --cc t/t4204-patch-id.sh
Simple merge

diff --cc t/test-lib-functions.sh
Simple merge