Check for messages with duplicate names inside a channel

Make sure there are not 2 messages with the same name in the
same channel.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>

python_modules/ptypes.py

@@ -1055,6 +1055,8 @@ class ChannelType(Type):
                     m.value = info.count
                 info.count = m.value + 1
                 info.messages.append(m)
+                if m.name in info.messages_byname:
+                    raise Exception("Duplicated message name '%s' in channel '%s'" % (m.name, self.name))
                 info.messages_byname[m.name] = m
 
         self.server_messages = server_info.messages