Improve handling when user has set username/password for a server, while the server doesn't need authentication.

For incorrect authentication, some servers return code '502 ... Access denied...' instead of the official '481' code.
Handle that as a bad login too.

sabnzbd/downloader.py

@@ -759,7 +759,7 @@ def clues_login(text):
     """ Check for any "failed login" clues in the response code
     """
     text = text.lower()
-    for clue in ('username', 'password', 'invalid', 'authen'):
+    for clue in ('username', 'password', 'invalid', 'authen', 'access denied'):
         if clue in text:
             return True
     return False

sabnzbd/newswrapper.py

@@ -280,6 +280,12 @@ class NewsWrapper(object):
         elif not self.user_ok:
             if code == '381':
                 self.user_ok = True
+            elif code == '281':
+                # No login required
+                self.user_ok = True
+                self.pass_sent = True
+                self.pass_ok = True
+                self.connected = True
 
         if self.user_ok and not self.pass_sent:
             command = 'authinfo pass %s\r\n' % (self.server.password)