PostgreSQL 9.1.0

* Allow synchronous replication
* Add support for foreign tables
* Add per-column collation support
* Add extensions which simplify packaging of additions to PostgreSQL
* Add a true serializable isolation level
* Support unlogged tables using the UNLOGGED option in CREATE TABLE
* Allow data-modification commands (INSERT/UPDATE/DELETE) in WITH clauses
* Add nearest-neighbor (order-by-operator) searching to GiST indexes
* Add a SECURITY LABEL command and support for SELinux permissions control
* Update the PL/Python server-side language