The fix is to give defaultLocale a dedicated mapping.  We can remove some static
SQL while we are at it.

For historical purposes:

<danpb> two different associations using the same mapping table, with different
cardinality just seems wrong
<justin> I haven't seen that yet.  Which associations?
<danpb> it complains every time generate-sql is run
<danpb> contentsection <-> locales and contentsection <-> default locale
<-- vadim has quit (Client Exiting)
<rhs> justin says he'll fix it