#451 PostgreSQLOidDataType.setSqlValue(): use connection.unwrap() to get PGConnection

[Jeff Jensen]

From MR 58 by @wbiller:
I ran into a ClassCastException when using the oid datatype and the HikariCP connection pool. The getSqlValue already uses connection.unwrap, so I gave it a try in in a custom implementation of setSqlValue, and it worked. That's why I decided to use connection.unwrap in setSqlValue as well.