DataFrame.to_string() does not always use formatters argument
``` python
In [28]: myformatter = lambda x: '[%4.1f]' % x

In [29]: df = pandas.DataFrame(np.random.randn(2,2), columns=['A', 'B'])

In [30]: df
Out[30]:
          A         B
0 -0.478634  1.143561
1  0.043301  1.006389

In [31]: print df.to_string(formatters={'A': myformatter})
       A         B
0 [-0.5]  1.143561
1 [ 0.0]  1.006389

In [32]: df = pandas.DataFrame(np.random.randint(0, 10, (2, 2)), columns=['A', 'B'])

In [33]: df
Out[33]:
   A  B
0  4  3
1  0  4

In [34]: print df.to_string(formatters={'A': myformatter})
   A  B
0  4  3
1  0  4

In [35]:

```
