Issue #2377: Make importlib the implementation of __import__().

importlib._bootstrap is now frozen into Python/importlib.h and stored
as _frozen_importlib in sys.modules. Py_Initialize() loads the frozen
code along with sys and imp and then uses _frozen_importlib._install()
to set builtins.__import__() w/ _frozen_importlib.__import__().
diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
index d9bef38..fa0d48c 100644
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -322,7 +322,7 @@
             self._coverage(tracer)
         if os.path.exists(TESTFN):
             files = os.listdir(TESTFN)
-            self.assertEqual(files, [])
+            self.assertEqual(files, ['_importlib.cover'])  # Ignore __import__
 
     def test_issue9936(self):
         tracer = trace.Trace(trace=0, count=1)