where broken after sort
Glad I hunted this one down. Was seeing some very weird stuff. Using 0.10.1

```
import pandas
names = ["a","b","c"]
df = pandas.DataFrame([[0,2,4],[2,0,7],[4,7,0]], index=names, columns=names)
df
#   a  b  c
#a  0  2  4
#b  2  0  7
#c  4  7  0

df2 = df.sort("b").T.sort("c").T
df.where(df <= 4, 0)
#   a  b  c
#a  0  2  4
#b  2  0  0
#c  4  0  0

df2.where(df <= 4, 0)
#   c  a  b
#b  7  2  0
#a  4  0  0
#c  0  0  7
```
