Merge branch 'zj/diff-empty-chmod'

Merge branch 'zj/diff-empty-chmod'

"git diff --stat" used to fully count a binary file with modified
execution bits whose contents is unmodified, which was not right.

By Zbigniew Jędrzejewski-Szmek (4) and Johannes Sixt (1)
* zj/diff-empty-chmod:
  t4006: Windows do not have /dev/zero
  diff --stat: do not run diff on indentical files
  diff --stat: report mode-only changes for binary files like text files
  tests: check --[short]stat output after chmod
  test: modernize style of t4006

Conflicts:
	diff.c