Merge branch 'rs/archive'

Merge branch 'rs/archive'

* rs/archive:
  archive - leakfix for format_subst()
  Define NO_MEMMEM on Darwin as it lacks the function
  archive: rename attribute specfile to export-subst
  archive: specfile syntax change: "$Format:%PLCHLDR$" instead of just "%PLCHLDR" (take 2)
  add memmem()
  Remove unused function convert_sha1_file()
  archive: specfile support (--pretty=format: in archive files)
  Export format_commit_message()