Issue #15715: Ignore failed imports triggered by the use of fromlist.

When the fromlist argument is specified for __import__() and the
attribute doesn't already exist, an import is attempted. If that fails
(e.g. module doesn't exist), the ImportError will now be silenced (for
backwards-compatibility). This *does not* affect
``from ... import ...`` statements.

Thanks to Eric Snow for the patch and Simon Feltman for reporting the
regression.

Lib/test/test_import.py

@@ -334,6 +334,12 @@ class ImportTests(unittest.TestCase):
             del sys.path[0]
             remove_files(TESTFN)
 
+    def test_bogus_fromlist(self):
+        try:
+            __import__('http', fromlist=['blah'])
+        except ImportError:
+            self.fail("fromlist must allow bogus names")
+
 
 class PycRewritingTests(unittest.TestCase):
     # Test that the `co_filename` attribute on code objects always points