Merge branch 'ab/attribute-format'

Many "printf"-like helper functions we have have been annotated
with __attribute__() to catch placeholder/parameter mismatches.

* ab/attribute-format:
  advice.h: add missing __attribute__((format)) & fix usage
  *.h: add a few missing __attribute__((format))
  *.c static functions: add missing __attribute__((format))
  sequencer.c: move static function to avoid forward decl
  *.c static functions: don't forward-declare __attribute__

diff --cc commit-graph.c
Simple merge

diff --cc imap-send.c
Simple merge

diff --cc merge-ort.c
Simple merge

diff --cc merge-recursive.c
Simple merge

diff --cc midx.c
Simple merge

diff --cc strbuf.h
Simple merge