[url] Add a guard for pytest calling the setup when it shouldn't.

url.py

@@ -41,8 +41,12 @@ def configure(config):
             'Prefix to suppress URL titling', '!')
 
 
-def setup(bot):
+def setup(bot=None):
     global url_finder, exclusion_char
+
+    if not bot:
+        return
+
     if bot.config.has_option('url', 'exclude'):
         regexes = [re.compile(s) for s in
                    bot.config.url.get_list(bot.config.exclude)]