this wasn't working (with a list of negative indicies), but pseudo deprecating ``icol`` anyhow (its fixed now in any event)
```
n [11]: df
Out[11]: 
          0         1         2         3
0  0.143576  0.957356  0.990652  0.852501
1  0.187392  0.722276  0.761076  0.037906
2  0.793335  0.975346  0.251745  0.616150
3  0.020577  0.438545  0.872616  0.491270
4  0.480611  0.318490  0.563682  0.994372
5  0.795428  0.786869  0.096081  0.300232

In [12]: df.icol([1,2])
Out[12]: 
          1         2
0  0.957356  0.990652
1  0.722276  0.761076
2  0.975346  0.251745
3  0.438545  0.872616
4  0.318490  0.563682
5  0.786869  0.096081

In [13]: df.icol([-1,-2])
Out[13]: 
    3         2
0 NaN  0.000000
1 NaN  0.990652
2 NaN  0.761076
3 NaN  0.251745
4 NaN  0.872616
5 NaN  0.563682

```