Use generic attribute management in PL/Python

Switch the implementation of the plan and result types to generic attribute
management, as described at <http://docs.python.org/extending/newtypes.html>.
This modernizes and simplifies the code a bit and prepares for Python 3.1,
where the old way doesn't work anymore.

src/pl/plpython/sql/plpython_spi.sql

@@ -87,3 +87,21 @@ SELECT join_sequences(sequences) FROM sequences
 	WHERE join_sequences(sequences) ~* '^A';
 SELECT join_sequences(sequences) FROM sequences
 	WHERE join_sequences(sequences) ~* '^B';
+
+
+--
+-- plan and result objects
+--
+
+CREATE FUNCTION result_nrows_test() RETURNS int
+AS $$
+plan = plpy.prepare("SELECT 1 UNION SELECT 2")
+plpy.info(plan.status()) # not really documented or useful
+result = plpy.execute(plan)
+if result.status() > 0:
+   return result.nrows()
+else:
+   return None
+$$ LANGUAGE plpythonu;
+
+SELECT result_nrows_test();