Merge branch 'sk/force-if-includes'

"git push --force-with-lease[=<ref>]" can easily be misused to lose
commits unless the user takes good care of their own "git fetch".
A new option "--force-if-includes" attempts to ensure that what is
being force-pushed was created after examining the commit at the
tip of the remote ref that is about to be force-replaced.

* sk/force-if-includes:
  t, doc: update tests, reference for "--force-if-includes"
  push: parse and set flag for "--force-if-includes"
  push: add reflog check for "--force-if-includes"

diff --cc builtin/push.c
Simple merge

diff --cc remote.c
Simple merge

diff --cc remote.h
Simple merge

diff --cc send-pack.c
Simple merge