Merge branch 'js/log-remerge-keep-ancestry'

"git log -p --remerge-diff --reverse" was completely broken.

* js/log-remerge-keep-ancestry:
  log: --remerge-diff needs to keep around commit parents

diff --cc builtin/log.c
Simple merge

diff --cc t/t4069-remerge-diff.sh
Simple merge