'IntegerArray' object has no attribute 'T'
In our case this arose via `.cumsum()`:
```
pd.Series([0, 1], dtype='int64').cumsum()
0    0
1    1
dtype: int64

pd.Series([0, 1], dtype='Int64').cumsum()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-31-2ebc3e3cf698> in <module>
----> 1 pd.Series([0, 1], dtype='Int64').cumsum()
...

~/model/.venv/lib/python3.7/site-packages/pandas/core/generic.py in na_accum_func(blk_values)
  11324                 np.putmask(result, mask, mask_b)
  11325             else:
> 11326                 result = accum_func(blk_values.T, axis)
  11327
  11328             # transpose back for ndarray, not for EA

AttributeError: 'IntegerArray' object has no attribute 'T'
```
But it's also true that just calling `.values.T` on a regular `int` array works (just a no-op), whereas on an `Int64` array it does not. Same is true for 

Any reason not to just add a no-op `.T` on the base ExtensionArray class..? cc @TomAugspurger in case you have an opinion 🙂 