Merge branch 'nd/diff-stat-with-summary'

Merge branch 'nd/diff-stat-with-summary'

"git diff" and friends learned "--compact-summary" that shows the
information usually given with the "--summary" option on the same
line as the diffstat output of the "--stat" option (which saves
vertical space and keeps info on a single path at the same place).

* nd/diff-stat-with-summary:
  diff: add --compact-summary
  diff.c: refactor pprint_rename() to use strbuf