message: contrib: Silence git-describe when looking for tag
  Otherwise, it prints a rather disturbing message to stderr:
  fatal: no tag exactly matches '<hash>'
diff: #
  # A helper script to be sourced into the gitian descriptors
  -if RECENT_TAG="$(git describe --exact-match HEAD)"; then
  +if RECENT_TAG="$(git describe --exact-match HEAD 2> /dev/null)"; then
  VERSION="${RECENT_TAG#v}"
  else
  VERSION="$(git rev-parse --short=12 HEAD)"
  