Added JDatabaseExporterPostgresql class. Added JDatabaseImporterPostgresql class. Added JDatabaseQueryPostgresql class. Added test classes for Postgresql's exporter. Added test classes for Postgresql's importer. Added test class for Postgresql driver. Added test class for Postgresql's query. Added DDL for Postgresql database. Added capability to use this driver with older Postgresql database (8.3, 8.4 and 9.0 versions). Updated tests, actually it's possible to test older database version for exporter and importer class changing return value of 'getVersion' inside setup() call. To test older database for driver class, just install it. Backward compatibility of getQuery, now returns query as JDatabaseQueryPostgresql only if requested by second argument. Use of getQuery() returning JDatabaseQueryPostgresql object is needed by insertid() call to properly work. Added isSupported() function and its test.