Make nbextension test a little clearer about the intent.

IPython/html/tests/test_nbextensions.py

@@ -103,7 +103,7 b' class TestInstallNBExtension(TestCase):'
             for file in self.files:
                 self.assert_installed(
                     pjoin(basename(self.src), file),
-                    ipdir
+                    user=bool(ipdir)
                 )
     
     def test_create_nbextensions_user(self):