pivot_table on non existent column
If you  try to access a column which doesn't exist you get an error

```
In [11]: df = pd.DataFrame([[1, 2, 3]], columns=list('ABC'))

In [12]: df.pivot_table('no', 'A', 'B')
DataError: No numeric types to aggregate
```

Should probably say that the column isn't there.

vaguely related #4733 ?
