The Postgres connection adapter assumed that was ever possible to disable referential integrity, causing problems when it was not possible.

Disabling referential integrity is possible when the Postgres user is a superuser. It can be verified with (SQL):

    SHOW is_superuser;

It was added a warning when the user is not a postgres superuser and it is not possible to disable referential integrity, to help the developer know about possible problems.

And now the adapter just commit the "disable trigger" SQL when it know it can be done.