GUC support. It's now possible to set datestyle, timezone, and
client_encoding from postgresql.conf and per-database or per-user
settings. Also, implement rollback of SET commands that occur in a
transaction that later fails. Create a SET LOCAL var = value syntax
that sets the variable only for the duration of the current transaction.
All per previous discussions in pghackers.
to reset session userid to the originally-authenticated name. Also,
relax SET SESSION AUTHORIZATION to allow specifying one's own username
even if one is not superuser, so as to avoid unnecessary error messages
when loading a pg_dump file that uses this command. Per discussion from
several months ago.
