PL/Python: Add cursor and execute methods to plan object

Instead of

    plan = plpy.prepare(...)
    res = plpy.execute(plan, ...)

you can now write

    plan = plpy.prepare(...)
    res = plan.execute(...)

or even

    res = plpy.prepare(...).execute(...)

and similarly for the cursor() method.

This is more in object oriented style, and makes the hybrid nature of
the existing execute() function less confusing.

Reviewed-by: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>

src/pl/plpython/plpy_cursorobject.c

@@ -25,7 +25,6 @@
 
 
 static PyObject *PLy_cursor_query(const char *query);
-static PyObject *PLy_cursor_plan(PyObject *ob, PyObject *args);
 static void PLy_cursor_dealloc(PyObject *arg);
 static PyObject *PLy_cursor_iternext(PyObject *self);
 static PyObject *PLy_cursor_fetch(PyObject *self, PyObject *args);
@@ -160,7 +159,7 @@ PLy_cursor_query(const char *query)
 	return (PyObject *) cursor;
 }
 
-static PyObject *
+PyObject *
 PLy_cursor_plan(PyObject *ob, PyObject *args)
 {
 	PLyCursorObject *cursor;