PL/Python: Adjust the regression tests for Python 3.3

The string representation of ImportError changed.  Remove printing
that; it's not necessary for the test.

The order in which members of a dict are printed changed.  But this
was always implementation-dependent, so we have just been lucky for a
long time.  Do the printing the hard way to ensure sorted order.

src/pl/plpython/sql/plpython_params.sql

@@ -14,7 +14,14 @@ $$ LANGUAGE plpythonu;
 
 CREATE FUNCTION test_param_names2(u users) RETURNS text AS $$
 assert u == args[0]
-return str(u)
+if isinstance(u, dict):
+    # stringify dict the hard way because otherwise the order is implementation-dependent
+    u_keys = list(u.keys())
+    u_keys.sort()
+    s = '{' + ', '.join([repr(k) + ': ' + repr(u[k]) for k in u_keys]) + '}'
+else:
+    s = str(u)
+return s
 $$ LANGUAGE plpythonu;
 
 -- use deliberately wrong parameter names