Fix scrapy#396 re-triggered issue

The InteractiveShellEmbed class is a singleton
and we need to drop the instance with its clear_instance() method
to rebuild the instance from scratch with fresh environment
for each subsequent drop in.

scrapy/utils/console.py

@@ -15,6 +15,9 @@ def wrapper(namespace=namespace, banner=''):
         config = load_default_config()
         # Always use .instace() to ensure _instance propagation to all parents
         # this is needed for <TAB> completion works well for new imports
+        # and clear the instance to always have the fresh env
+        # on repeated breaks like with inspect_response()
+        InteractiveShellEmbed.clear_instance()
         shell = InteractiveShellEmbed.instance(
             banner1=banner, user_ns=namespace, config=config)
         shell()