TST: assert_series/frame not comparing for categoricals
xref https://github.com/dask/partd/pull/7

```
In [1]: df1 = DataFrame({'A' : Series(list('aba')).astype('category', categories=list('ab'), ordered=True)})

In [2]: df2 = DataFrame({'A' : Series(list('aba')).astype('category', categories=list('ba'), ordered=True)})

In [3]: tm.assert_frame_equal(df1, df2)

In [11]: df2 = DataFrame({'A' : Series(list('aba')).astype('category', categories=list('ab'), ordered=False)})

In [12]: tm.assert_frame_equal(df1, df2)

In [13]: df2 = DataFrame({'A' : Series(list('aba')).astype('category', categories=list('ba'), ordered=False)})

In [14]: tm.assert_frame_equal(df1, df2)
```

all of these should fail as the ordered categoricals don't compare equal in the categories, and ordered is not being compared (nor categories)

Furthermore the `assert_series_equal` fail for the same.

`assert_categorical_equal` DOES the right thing, but not being called here. (not that this _should_ say `categories` are not equal?)

```
In [17]: tm.assert_categorical_equal(df1.A.values, df2.A.values)
AssertionError: Index are different

Index values are different (100.0 %)
[left]:  Index([u'a', u'b'], dtype='object')
[right]: Index([u'b', u'a'], dtype='object')
```
