message: rel-builds: Specify core.abbrev for git-rev-parse
  Chose 12 because the kernel uses it:
  And also because it's a nice number.
diff: if RECENT_TAG="$(git describe --exact-match HEAD)"; then
  VERSION="${RECENT_TAG#v}"
  else
  - VERSION="$(git rev-parse --short HEAD)"
  + VERSION="$(git rev-parse --short=12 HEAD)"
  fi
  DISTNAME="bitcoin-${VERSION}"
  