DataFrame.interpolate(axis=1, method="time", inplace=True) 
In pandas 0.15.2, DataFrame.interpolate( ... ) doesn't work with the keyword combination axis=1, method="time", inplace=True. It just returns the original DataFrame.

```
import pandas as pd
import numpy as np

periods=5
idx = pd.date_range(start="2014-01-01", periods=periods)
data = np.random.rand(periods, periods)
data[data < 0.5] = np.nan
df0 = pd.DataFrame(index=idx, columns=idx, data=data)
df1 = df0.copy()

print "(1) Original df"
print df0

print "\n(2a) axis=0, inplace=False"
print df0.interpolate(axis=0, method="time")
print "\n(2b) axis=0, inplace=True"
df0.interpolate(axis=0, method="time", inplace=True)
print df0

print "\n(3a) axis=1, inplace=False"
print df1.interpolate(axis=1, method="time")
print "\n(3b) axis=1, inplace=True"
df1.interpolate(axis=1, method="time", inplace=True)
print df1
```
