index_col parser bug
```
In [10]: !cat book_scripts/io/ex2.csv
1,2,3,4,hello
5,6,7,8,world
9,10,11,12,foo
In [11]: names
Out[11]: ['a', 'b', 'c', 'd', 'message']

In [12]: read_csv('book_scripts/io/ex2.csv', names=names, index_col=['message'])
Out[12]: 
         a   b   c   d
message               
hello    1   2   3   4
world    5   6   7   8
foo      9  10  11  12

In [13]: read_csv('book_scripts/io/ex2.csv', names=names, index_col='message')
Out[13]: 
       a   b   c   d
hello  1   2   3   4
world  5   6   7   8
foo    9  10  11  12
```
