string to date format ignored on apply
_From the [So question](http://stackoverflow.com/questions/16672237/specifying-date-format-when-converting-with-pandas-to-datetime)._

I think apply be passing on the format keyword argument:

```
In [1]: s = pd.Series(['12/1/2012', '30/01/2012'])

In [2]: s.apply(pd.to_datetime, format='%d/%m/%Y')
Out[2]:
0   2012-12-01 00:00:00
1   2012-01-30 00:00:00
dtype: datetime64[ns]

In [3]: pd.to_datetime(s, format='%d/%m/%Y')
Out[3]:
0   2012-01-12 00:00:00
1   2012-01-30 00:00:00
dtype: datetime64[ns]
```
