Do some cleanup in importlib:

+ Ditch using arguments to super().
+ Ditch subclassing from object directly.
+ Move directory check out of chaining path hook to file path hook/finder.
+ Rename some classes to better reflect they are finders, not importers.

Lib/importlib/test/source/test_path_hook.py

@@ -10,7 +10,7 @@ class PathHookTest(unittest.TestCase):
     def test_success(self):
         # XXX Only work on existing directories?
         with source_util.create_modules('dummy') as mapping:
-            self.assert_(hasattr(importlib.FileImporter(mapping['.root']),
+            self.assert_(hasattr(importlib.FileFinder(mapping['.root']),
                                  'find_module'))