Merge branch 'mp/rebase-label-length-limit'

Overly long label names used in the sequencer machinery are now
chopped to fit under filesystem limitation.

* mp/rebase-label-length-limit:
  rebase: allow overriding the maximal length of the generated labels
  sequencer: truncate labels to accommodate loose refs

diff --cc git-compat-util.h
Simple merge

diff --cc sequencer.c
Simple merge