Patch for /trunk/lib/backtest.py

```
plot cannot be shown and prevents any other plots from showing. try plt.show() 
under plottrades
```

Original issue reported on code.google.com by `laur.laa...@gmail.com` on 25 Feb 2015 at 5:34

Attachments:
- [backtest.py.patch](https://storage.googleapis.com/google-code-attachments/trading-with-python/issue-4/comment-0/backtest.py.patch)
