pydata/pandas — pull request #7768 by JanSchulz (2014-07-16 18:42:14+00:00)
Title: Categorical: preserve ints when NaN are present

`Categorical([1, np.nan])` would end up with a single `1.` float level.
This commit ensures that if `values` is a list of ints and contains np.nan,
the float conversation does not take place.