Raise TypeError if the name given to importlib.__import__() lacks an rpartition

attribute. Was throwing AttributeError before. Discovered when running
test_builtin against importlib.

This exception change is specific to importlib.__import__() and does not apply to
import_module() as it is being done for compatibility reasons only.

Lib/importlib/_bootstrap.py

@@ -917,6 +917,8 @@ def __import__(name, globals={}, locals={}, fromlist=[], level=0):
     import (e.g. ``from ..pkg import mod`` would have a 'level' of 2).
 
     """
+    if not hasattr(name, 'rpartition'):
+        raise TypeError("module name must be str, not {}".format(type(name)))
     if level == 0:
         module = _gcd_import(name)
     else: