PERF: stop allocating the string "id" over and over
Improving disabling integrity of PostgreSQL

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 superuser. It can be verified with (SQL):

    SHOW is_superuser;

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

No need to commit SQL that we know will fail