Update PostgreSQL binary (bytea) handling and improve connection performance

PostgreSQL driver requires multiple queries when a connection to the database is made. These can be handled differently to remove the query requirement.

PostgreSQL 9.1 is now the minimum required version, so the escape_format can be forced to the new hex format. This has performance and functionality improvements when using pg_query_params(). Functions that did not support BLOBS before can now.

normalise_value() can now easily escape BLOBS the same as other fields. This allows a more simplified driver.

pg_field_type() on a result does not require a db query as it's stored in the result set. So the type can be compared to bytea rather than getting the OID, having to pass it around and match it.

get_field_sql() did not support BLOB's on PostgreSQL, even though they worked on mysql. With the new formatting they now work.