"git diff --color-moved --cc --stat -p" did not work well due to
funny interaction between a bug in color-moved and the rest, which
has been fixed.

* jk/diff-cc-stat-fixes:
  combine-diff: treat --dirstat like --stat
  combine-diff: treat --summary like --stat
  combine-diff: treat --shortstat like --stat
  combine-diff: factor out stat-format mask
  diff: clear emitted_symbols flag after use
  t4006: resurrect commented-out tests