bug in row slicing in df.ix
pandas 0.9.1
when slicing rows using df.ix[], it returns more rows than it should

In [2]: df=DataFrame({'a':range(5),'b':range(5)})
In [3]: df.ix[1:3,:]    # should return rows 1,2
Out[3]: 
   a  b
1  1  1
2  2  2
3  3  3     # this last row should not here
