Remove the import hook when unloading the old pkg_resources modules

--HG--
branch : agronholm/remove-the-import-hook-when-unloading-th-1458177009332

ez_setup.py

@@ -192,6 +192,11 @@ def _conflict_bail(VC_err, version):
 
 
 def _unload_pkg_resources():
+    from pkg_resources.extern import VendorImporter
+    sys.meta_path = [importer for importer in sys.meta_path if
+                     not isinstance(importer, VendorImporter)]
+    del VendorImporter
+
     del_modules = [
         name for name in sys.modules
         if name.startswith('pkg_resources')