Merge branch 'jc/sequencer-stopped-sha-simplify'

Recently the format of an internal state file "rebase -i" uses has
been tightened up for consistency, which would hurt those who start
"rebase -i" with old git and then continue with new git.  Loosen
the reader side a bit (which we may want to tighten again in a year
or so).

* jc/sequencer-stopped-sha-simplify:
  sequencer: tolerate abbreviated stopped-sha file

diff --cc sequencer.c
Simple merge