Perhaps we should also trim the table of infrequently used types.
This issue was exposed in #153. I don't like the fact that this change means the information in the static table doesn't entirely agree with what would otherwise be fetched dynamically by the Database.PostgreSQL.Simple.TypeInfo module, but this does appear to be a special case, and handling it here does seem to be less worse then handling it there. Plus, now GenTypeInfo should be able to deal with array types, so we probably should strongly consider moving at least some of them into the static table.
In preparation for the pure escaping routines discussed in #120