riplike: TypeError

```
C.MW.2011.111848.MF501781.23.2_441
Traceback (most recent call last):
  File "riplike.py", line 203, in <module>
    main()
  File "riplike.py", line 192, in main
    results = riplike(s, reference, window=args.window, step=args.step, nrep=args.nrep)
  File "riplike.py", line 117, in riplike
    ndiff = sum(s2)
TypeError: unsupported operand type(s) for +: 'int' and 'str'
```