postgres not detected correctly in set_db_timezone function

In the function set_db_timezone of the file date_api_sql.inc, postgres is not being detected correctly; the wrong boolean operator is being used in when checking the version of mysql so that all versions of postgres are also caught by that case.

I've attached a short patch which changes the boolean to the correct && from || and adjusts the syntax used for setting the timezone in postgres to SET TIME ZONE INTERVAL '$offset' HOURS TO MINUTES to match the postgres manual.