string truncation when using Series.astype(str)
When converting a pandas Series object to type string using `astype(str)`, long strings are truncated to 64 characters silently.

Pandas version:  0.12
Numpy version:  1.7.1

``` python

In [1]: s = '0123456789' * 10

In [2]: tmp = np.array([s]).astype(str)
         tmp
Out[2]: array([ '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'], 
      dtype='|S100')

In [3]: tmp = pd.Series([s]).astype(str)
       tmp[0]
Out[3]: '0123456789012345678901234567890123456789012345678901234567890123'

In [4]: len(tmp[0])
Out[4]: 64
```
