Integer column formatting a bit off
Completely my fault when I refactored the to_string code recently 

```
  ticker      date  pnl    mv
0   aapl  01/01/12  100  1000
1   aapl  01/02/12  -50   950
2   aapl  01/03/12  200  1150
3   goog  01/01/12  100  2000
4   goog  01/02/12  100  2100
5   goog  01/03/12  -50  2050
6   goog  01/04/12  -50   200
```
