Trying to import a submodule from another module and not a package was raising
AttributeError in importlib when it should be an ImportError.

Found when running importlib against test_runpy.
diff --git a/Misc/NEWS b/Misc/NEWS
index 608e9a8..bc7f5b0 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -68,6 +68,9 @@
 Library
 -------
 
+- Trying to import a submodule from a module that is not a package, ImportError
+  should be raised, not AttributeError.
+
 - When the globals past to importlib.__import__() has __package__ set to None,
   fall back to computing what __package__ should be instead of giving up.