BUG: read_csv() does strange things if data rows have trailing delimiter
Given a file `t.txt` like this:

```
A,B,C
1,4,7,
2,5,8,
3,6,9,
```

`pandas.read_csv('t.txt')` produces:

```
   A  B   C
1  4  7 NaN
2  5  8 NaN
3  6  9 NaN
```

In other words, it implies a nonexistent header column for what it believes is the index.  I would expect it to do the same as this code:

```
pd.read_csv('t.txt', index_col=False).set_index('A')
```

Which is:

```
   B  C
A      
1  4  7
2  5  8
3  6  9
```

The first example has the same problem even if you specify `index_col=0`, which is confusing because saying the first column should be used as the index is pretty much what's being done in the second example.

Files like this are commonly produced by vendors like Bloomberg whose formats we cannot expect to change.

Pandas 0.18.1.
