PERF/API: Treat series as array-like for rename_categories

HEAD:

```
[ 50.00%] ··· Running categoricals.Categoricals3.time_rank_string_cat          6.63ms
[ 50.00%] ·····
[100.00%] ··· Running categoricals.Categoricals3.time_rank_string_cat_ordered  4.85ms
```

Closes pandas-dev#17981

Author: TomAugspurger

pandas/core/categorical.py

@@ -900,7 +900,8 @@ def rename_categories(self, new_categories, inplace=False):
         inplace = validate_bool_kwarg(inplace, 'inplace')
         cat = self if inplace else self.copy()
 
-        if is_dict_like(new_categories):
+        if (is_dict_like(new_categories) and
+                not isinstance(new_categories, ABCSeries)):
             cat.categories = [new_categories.get(item, item)
                               for item in cat.categories]
         else:

pandas/tests/test_categorical.py

@@ -1203,6 +1203,13 @@ def test_rename_categories(self):
         with pytest.raises(ValueError):
             cat.rename_categories([1, 2])
 
+    def test_rename_categories_series(self):
+        # https://github.com/pandas-dev/pandas/issues/17981
+        result = pd.Categorical(['a', 'b']).rename_categories(
+            pd.Series([0, 1]))
+        expected = pd.Categorical([0, 1])
+        tm.assert_categorical_equal(result, expected)
+
     def test_rename_categories_dict(self):
         # GH 17336
         cat = pd.Categorical(['a', 'b', 'c', 'd'])