ENH: Series Creation Does Not Intelligently Handle datetime.date
For example:

```
In [77]: pd.Series([datetime.datetime(2012, 1, 1)]).dtype
Out[77]: dtype('<M8[ns]')
```

works as expected.

However:

```
In [78]: pd.Series([datetime.date(2012, 1, 1)]).dtype
Out[78]: dtype('O')
```

create a Series of type object rather than datetime64.

You can get the desired effect:

```
In [89]: pd.Series(np.array([np.datetime64(datetime.date(2012, 1, 1))])).dtype
Out[89]: dtype('<M8[D]')
```
