read_csv backwards compatibility: set header to None when names is passed
Given the awesome work on read_csv() pending for 0.10, this may be a necessary change, however, for backwards compatibility, can the `names` parameter change to implicitly set `header` to None again?  The new behavior of `names` is clearly documented, so feel free to reject as the new default.

Up to and including 0.9.1, specifying the names parameter implied the first row is data, not header.

```
In [1]: pd.__version__
Out[1]: '0.9.1'

In [2]: pd.read_csv("sample.csv", names=['c0', 'c1'])
Out[2]: 
     c0     c1
0  abcd  efghi
1   jkl   mnop
```

It came as a surprise that this no longer worked -- easily worked around though.

```
In [1]: pd.__version__
Out[1]: '0.10.0b1'

In [2]: pd.read_csv("sample.csv", names=['c0', 'c1'])
Out[2]: 
    c0    c1
0  jkl  mnop

In [3]: pd.read_csv("sample.csv", names=['c0', 'c1'], header=None)
Out[3]: 
     c0     c1
0  abcd  efghi
1   jkl   mnop
```
