Internals .apply Methods
`core.internals.BlockManager.isna` has what appears to be a [typo](https://github.com/pandas-dev/pandas/blob/master/pandas/core/internals.py#L3296):
```
    def isna(self, **kwargs):
        return self.apply('apply', **kwargs)
```

The pattern in all of the other methods like this would be `self.apply('isna', **kwargs)`.  But in trying to apply what looks like a simple fix, other breakages show up:

```
df = pd.DataFrame([[0, np.nan],[ np.nan, 1]], columns=list('AB')) 
mgr = df._data

>>> mgr.diff()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3209, in diff
    return self.apply('diff', **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3091, in apply
    applied = getattr(b, f)(**kwargs)
TypeError: diff() takes at least 2 arguments (2 given)

>>> mgr.diff(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: diff() takes exactly 1 argument (2 given)

>>> mgr.diff(axis=0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3209, in diff
    return self.apply('diff', **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3091, in apply
    applied = getattr(b, f)(**kwargs)

>>> mgr.quantile()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3200, in quantile
    return self.reduction('quantile', **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pandas/core/internals.py", line 3129, in reduction
    axe, block = getattr(b, f)(axis=axis, **kwargs)
TypeError: quantile() takes at least 2 arguments (3 given)
>>> mgr.quantile(.5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: quantile() takes exactly 1 argument (2 given)
```
 
I don't see tests for these methods in `tests.test_internals`, and it isn't obvious if/where they are actually used.  Trying to track down coverage stats now (the codecov badge on the github page doesn't link to codecov.   Could've sworn that used to work...)