Fix when is 'self' used as a parameter name in Python

Fix corner case for variable names called 'self' after merging in patch #201

Examples/test-suite/keyword_rename.i

@@ -35,6 +35,10 @@ KW(chan, fallthrough)
 KW(end, function)
 KW(nil,local)
 
+struct Keywords {
+  void selfkw(int self) {}
+};
+
 %}