BUG: parser can handle a common_format multi-column index (no row index cols), (GH4702)

closes #4702, should help with #5254

Will handle the format generated by ``to_csv`` (which has a an 'extra' line for the index names)
and the more 'common' format

```
In [4]:         data = """,a,a,a,b,c,c
   ...: ,q,r,s,t,u,v
   ...: one,1,2,3,4,5,6
   ...: two,7,8,9,10,11,12"""

In [6]: read_csv(StringIO(data),header=[0,1],index_col=0)
Out[6]: 
     a         b   c    
     q  r  s   t   u   v
one  1  2  3   4   5   6
two  7  8  9  10  11  12
```       
equiv to
```
df = DataFrame([[1,2,3,4,5,6],[7,8,9,10,11,12]],
                       index=['one','two'],
                       columns=MultiIndex.from_tuples([('a','q'),('a','r'),('a','s'),
                                                  ('b','t'),('c','u'),('c','v')]))
```

no index col
```
In [1]: data = """a,a,a,b,c,c
   ...: q,r,s,t,u,v
   ...: 1,2,3,4,5,6
   ...: 7,8,9,10,11,12"""

In [2]: read_csv(StringIO(data),header=[0,1],index_col=None)
Out[2]: 
   a         b   c    
   q  r  s   t   u   v
0  1  2  3   4   5   6
1  7  8  9  10  11  12
```