sort_index is different from before version
```python
dates = pd.date_range('20170101', periods=6)
df = pd.DataFrame(np.random.randn(6,4), index=dates, columns=list('ABCD'))
print(df.sort_index())
```
####  version 1 output
D         C         B         A
2017-01-01 -1.418768  0.441179  0.668193 -0.883575
2017-01-02 -0.642718  0.406244 -1.558845 -0.050165
2017-01-03 -0.492745 -1.578937  0.829258 -1.092268
2017-01-04  1.113140 -2.376751  0.608188 -0.080518
2017-01-05  1.003710  1.969951 -1.583741 -0.610659
2017-01-06 -0.154932 -0.375000  0.179116 -0.294583

#### Expected Output
```
                 D        C      B       A
2017-01-01  0.426359  2.542352 -0.324047  0.418973
2017-01-02 -0.834625 -1.356709  0.150744 -1.690500
2017-01-03 -0.018274  0.900801  1.072851  0.149830
2017-01-04 -1.075027 -0.889379 -0.663223 -1.404002
2017-01-05 -1.273966 -1.335761 -1.356561 -1.135199
2017-01-06 -1.590793  0.693430 -0.504164  0.143386
```

