Added support PostgreSQL schema

[racklin]

PostgreSQL adapter will execute "SET search_path TO '???'" statement when connectted if schema is setting in config.

Ex:

$configPostgresql = array(
  'host' => '127.0.0.1',
  'username' => 'postgres',
  'password' => '',
  'dbname' => 'phalcon_test',
  'schema' => 'public'
);

$connection = new Phalcon\Db\Adapter\Pdo\Postgresql($configPostgresql);

Signed-off-by: Rack Lin racklin@gmail.com

[travisbot]

This pull request passes (merged d730c08 into bade2e9).

[phalcon]

Thanks racklin for your help!