PostgreSQL: last_insert_id uses select_value rather than using @connection.exec directly.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2998 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -305,12 +305,12 @@ module ActiveRecord
         execute "DROP INDEX #{index_name}"
       end      
 
-      
+
       private
         BYTEA_COLUMN_TYPE_OID = 17
 
         def last_insert_id(table, sequence_name)
-          Integer(@connection.exec("SELECT currval('#{sequence_name}')")[0][0])
+          Integer(select_value("SELECT currval('#{sequence_name}')"))
         end
 
         def select(sql, name = nil)