Test clean-up.

* jc/diff-test-updates:
  test_ln_s_add: refresh stat info of fake symbolic links
  t4008: modernise style
  t/diff-lib: check exact object names in compare_diff_raw
  tests: do not borrow from COPYING and README from the real source
  t4010: correct expected object names
  t9300: correct expected object names
  t4008: correct stale comments