to_clipboard issue with float_format
Related to #9448, using the following example:

```
In [143]: df = pd.DataFrame(np.random.randn(5,2), columns=['A', 'B'])

In [144]: df
Out[144]:
          A         B
0 -1.151315 -2.174735
1 -1.031375 -1.957344
2 -0.619368 -0.835133
3  2.562381 -0.294245
4  2.432353  0.032805
```

`to_clipboard` is said to pass the `kwargs` to `to_csv` (see docs: http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_clipboard.html). However, that seems not be fully true for the `float_format` kwarg:

```
df.to_clipboard(float_format='%.3f')
->
    A   B
0   -1.151  -2.175
1   -1.031  -1.957
2   -0.619  -0.835
3   2.562   -0.294
4   2.432   0.033
```

Now using a callable:

```
df.to_clipboard(float_format='{:.3f}'.format)
->
       A      B
0 -1.151 -2.175
1 -1.031 -1.957
2 -0.619 -0.835
3  2.562 -0.294
4  2.432  0.033
```

but this does not work with `to_csv`:

```
In [150]: df.to_csv(float_format='{:.3f}'.format)
---------------------------------------------------------------------------
TypeError: unsupported operand type(s) for %: 'builtin_function_or_method' and 'float'
```

Furthermore, when using a function as `float_format`, the result is no longer pastable in excel, even with `excel=True` (the default).
