message: Support perforce-style diffs in determining modified line ranges.
diff: @@ -65,12 +65,21 @@ BEGIN {
  active_range = 0;
  }
  +# seen in 'git diff'
  # diff before-file after-file
  /^diff/ {
  auto_flush_range();
  expect_filename = 1;
  }
  +# seen in 'p4 diff'
  +# ==== //depot/...#N - /local/path/to/file ====
  +/^==== .* ====$/ {
  + auto_flush_range();
  + expect_filename = 1;
  +}
  +
  +
  # + lines are after change only
  /^+/ {
  if (!expect_filename) {
  