slicing dataframe with date index is not working properly
When slicing data time - indexed dataframe with date in string format, it works:

```
df.ix['2014-11-12'].head()
Out[55]: 
                     calories      gsr  heart-rate  skin-temp  steps
date                                                                
2014-11-12 00:00:00       2.1  7.04640         NaN    85.7750     30
2014-11-12 00:01:00       1.5  7.40759         NaN    85.7375      0
2014-11-12 00:02:00       1.4  7.46220          49    85.5500      0
2014-11-12 00:03:00       1.4  7.55800         NaN    85.5500      0
2014-11-12 00:04:00       1.5  7.52163         NaN    85.5125      0
```

But when i try it with a date object, of datetime class , it slices only for time 00:00:00. 

```
d1=datetime.date(2014,11,12)
df.ix[d1]
Out[57]: 
calories       2.1000
gsr            7.0464
heart-rate        NaN
skin-temp     85.7750
steps         30.0000
Name: 2014-11-12 00:00:00, dtype: float64
```
