Merge branch 'ag/rebase-update-refs-limit-to-branches'

"git rebase --update-refs", when used with an rebase.instructionFormat
with "%d" (describe) in it, tried to update local branch HEAD by
mistake, which has been corrected.

* ag/rebase-update-refs-limit-to-branches:
  rebase: ignore non-branch update-refs

diff --cc sequencer.c
Simple merge

diff --cc t/t3404-rebase-interactive.sh
Simple merge