List of currencies is not retrieved on holidays

Today, the last csv column contains non-numeric values because it is a official holiday.

To account for these, the app now tries to select the column that makes more sense, going backwards day for day.

![Screenshot from 2013-03-30 07:38:03](https://f.cloud.github.com/assets/1790638/319986/79d4a5b2-9904-11e2-99ba-53b6c6be6fa6.png)