Bug in read_csv when passing header kwarg?
Seems to lose a row when passing a list as header, check it out:

```
>>> from StringIO import StringIO
>>> import pandas
>>> text = """
a  a  a  b  c  c
q r s t u v
1 2 3 4 5 6
1 2 3 4 5 6
"""
>>> # expected behavior without header
>>> pandas.read_csv(StringIO(text.strip()), sep='\s+')
   a a.1 a.2  b  c c.1
0  q   r   s  t  u   v
1  1   2   3  4  5   6
2  1   2   3  4  5   6
>>> #drops row  with specified header
>>> pandas.read_csv(StringIO(text.strip()), sep='\s+', header=[0, 1])
   (a, q)  (a, r)  (a, s)  (b, t)  (c, u)  (c, v)
0       1       2       3       4       5       6
>>> pandas.read_csv(StringIO(text.strip()), sep='\s+', header=[0, 1], tupleize_cols=False)
   a        b  c
   q  r  s  t  u  v
0  1  2  3  4  5  6
```
