 util.testing.assert_almost_equal() gives Key Error 
Test 1 works successfully with a square dataframe

``` python
import numpy as np
import pandas as pd

np.random.seed(1)
a = pd.DataFrame(np.random.rand(5, 5))
np.random.seed(1)
b = pd.DataFrame(np.random.rand(5, 5))
b += 0.00001
pd.util.testing.assert_almost_equal(a,b)
```

Test 2 fails with a dataframe where number rows > number of columns

``` python
np.random.seed(1)
a = pd.DataFrame(np.random.rand(6, 5))
np.random.seed(1)
b = pd.DataFrame(np.random.rand(6, 5))
b += 0.00001
pd.util.testing.assert_almost_equal(a,b)
```

KeyError: 5L
