Merge branch 'mg/status-v-v'

Merge branch 'mg/status-v-v'

"git status" now allows the "-v" to be given twice to show the
differences that are left in the working tree not to be committed.

* mg/status-v-v:
  commit/status: show the index-worktree diff with -v -v
  t7508: test git status -v
  t7508: .gitignore 'expect' and 'output' files