if (FOO=FOO; unset FOO) >/dev/null 2>&1; then
  as_unset=unset
else
  as_unset=false
fi

$as_unset VERSION_CONTROL SIMPLE_BACKUP_SUFFIX

if test "${VERSION_CONTROL+set}" = set; then
  echo "$0: the VERSION_CONTROL envvar is set --" \
    ' unset it and rerun this test' >&2
  exit 1
fi

if test "${SIMPLE_BACKUP_SUFFIX+set}" = set; then
  echo "$0: the SIMPLE_BACKUP_SUFFIX envvar is set --" \
    ' unset it and rerun this test' >&2
    >&2
  exit 1
fi