Add function name to PyArg_ParseTuple()

This causes the supplied function name to appear in any error message,
making the error message friendlier and relieving us from having to
provide our own in some cases.

src/pl/plpython/plpy_cursorobject.c

@@ -406,7 +406,7 @@ PLy_cursor_fetch(PyObject *self, PyObject *args)
 	volatile ResourceOwner oldowner;
 	Portal		portal;
 
-	if (!PyArg_ParseTuple(args, "i", &count))
+	if (!PyArg_ParseTuple(args, "i:fetch", &count))
 		return NULL;
 
 	cursor = (PLyCursorObject *) self;

src/pl/plpython/plpy_planobject.c

@@ -114,12 +114,11 @@ PLy_plan_dealloc(PyObject *arg)
 static PyObject *
 PLy_plan_status(PyObject *self, PyObject *args)
 {
-	if (PyArg_ParseTuple(args, ""))
+	if (PyArg_ParseTuple(args, ":status"))
 	{
 		Py_INCREF(Py_True);
 		return Py_True;
 		/* return PyInt_FromLong(self->status); */
 	}
-	PLy_exception_set(PLy_exc_error, "plan.status takes no arguments");
 	return NULL;
 }

src/pl/plpython/plpy_plpymodule.c

@@ -323,7 +323,7 @@ PLy_quote_literal(PyObject *self, PyObject *args)
 	char	   *quoted;
 	PyObject   *ret;
 
-	if (!PyArg_ParseTuple(args, "s", &str))
+	if (!PyArg_ParseTuple(args, "s:quote_literal", &str))
 		return NULL;
 
 	quoted = quote_literal_cstr(str);
@@ -340,7 +340,7 @@ PLy_quote_nullable(PyObject *self, PyObject *args)
 	char	   *quoted;
 	PyObject   *ret;
 
-	if (!PyArg_ParseTuple(args, "z", &str))
+	if (!PyArg_ParseTuple(args, "z:quote_nullable", &str))
 		return NULL;
 
 	if (str == NULL)
@@ -360,7 +360,7 @@ PLy_quote_ident(PyObject *self, PyObject *args)
 	const char *quoted;
 	PyObject   *ret;
 
-	if (!PyArg_ParseTuple(args, "s", &str))
+	if (!PyArg_ParseTuple(args, "s:quote_ident", &str))
 		return NULL;
 
 	quoted = quote_identifier(str);

src/pl/plpython/plpy_spi.c

@@ -51,7 +51,7 @@ PLy_spi_prepare(PyObject *self, PyObject *args)
 	volatile ResourceOwner oldowner;
 	volatile int nargs;
 
-	if (!PyArg_ParseTuple(args, "s|O", &query, &list))
+	if (!PyArg_ParseTuple(args, "s|O:prepare", &query, &list))
 		return NULL;
 
 	if (list && (!PySequence_Check(list)))