ENH/BUG: pd.read_csv(): usecols does not work when also using skipfooter
Steps to reproduce:

``` python
>>> import pandas as pd
>>> pd.__version__
'0.10.1'
>>> import StringIO
>>> data = 'a,b,c,d\n1,2,3,foo\n4,5,6,bar\n7,8,9,baz'
>>> df = pd.read_csv(StringIO.StringIO(data), usecols=[1])
>>> df
   b
0  2
1  5
2  8
>>> df = pd.read_csv(StringIO.StringIO(data), usecols=[1], skipfooter=1)
>>> df
   a  b  c    d
0  1  2  3  foo
1  4  5  6  bar
```
