Parser bug fix:  Make sure the table constraints allowed by prior releases
can still be parsed, even if they are technically not allowed by the
syntax diagram.  This is a cherry-pick of
[a1c014d8a87c8940b3], [38bf90af1ede6ee64e], and [e536ac041815b118c4].

FossilOrigin-Name: 28aed847c6a9d5a3eae4627e1c23eb5cb9c3aabe