pd.Catagorical breaks to_msgpack

[kay1793]

df=pd.DataFrame([[1,'John P. Doe'],[2,'Jane Dove'],[1,'John P. Doe']])
df[1]=pd.Categorical(df[1])
pd.read_msgpack(df.to_msgpack())
KeyError: 100

#8626, #8624

[jreback]

named in #7621 so master issue for this

[iorilu]

df=pd.DataFrame([[1,'John P. Doe'],[2,'Jane Dove'],[1,'John P. Doe']])
df[1]=pd.Categorical(df[1])
pd.read_msgpack(df[1].to_msgpack())

seems can't do msgpack on a series with category type
get error :
ValueError: cannot specify a dtype with a Categorical unless dtype='category'