Comment 9 for bug 1525682

Actually it turns out we really shouldn't be using the ${} syntax anyway, because if nettle is not present we end up printing
"nettle: no ()"
because $nettle is set to "no", not null or unset. So we should just write this out like:
if test "$nettle" = "yes"; then
    echo "nettle $nettle ($nettle_version)"
else
    echo "nettle $nettle"
fi