The test suite found a bug; select_ can fail now because a uniqueness
constrain has been added.
Now the test suite passes.
Also, I'm satisfied the changed PersistField instances work.
Looking over what changed, and what I've already tested, Key, FilePath,
and InodeCache are known working; ContentIdentifier is trivial
ByteString to blob; and SSha is trivial String to varchar. Both are
tested by the test suite. I've also tested the new FileSize and
EpochTime instances already, and they work.