Merge branch 'rj/add-p-pager'

A 'P' command to "git add -p" that passes the patch hunk to the
pager has been added.

* rj/add-p-pager:
  add-patch: render hunks through the pager
  pager: introduce wait_for_pager
  pager: do not close fd 2 unnecessarily
  add-patch: test for 'p' command

diff --cc add-patch.c
Simple merge

diff --cc t/t3701-add-interactive.sh
Simple merge