Include OID explicitly in the SELECT clause for older Postgres databases.

[resolves #680][resolves #670]

Author: HyunsangHan

src/main/java/io/r2dbc/postgresql/codec/PostgresTypes.java

@@ -40,7 +40,7 @@ public class PostgresTypes {
     public final static int NO_SUCH_TYPE = -1;
 
     // parameterized with %s for the comparator (=, IN), %s for the actual criteria value and %s for a potential LIMIT 1 statement
-    private static final String SELECT_PG_TYPE = "SELECT pg_type.* "
+    private static final String SELECT_PG_TYPE = "SELECT pg_type.oid, pg_type.* "
         + "  FROM pg_catalog.pg_type "
         + "  LEFT "
         + "  JOIN (select ns.oid as nspoid, ns.nspname, r.r "