BUG: read_csv: dtype={'id' : np.str}: Datatype not understood
I have a CSV with several columns. The first of which is a field called `id` with entries of the type `0001`, `0002`, etc. 

When loading this file, the following works:

``` python
pd.read_csv(my_path, dtype={'id' : np.int})
```

but the following doesn't:

``` python
pd.read_csv(my_path, dtype={'id' : np.str})
```

nor does this either:

``` python
pd.read_csv(my_path, dtype={'id' : str})
```

I get: `Datatype not understood`

This is with `pandas-0.10.1`
