Intentionally ignore alert messages.

Currently, the reference client bans peers that send alerts not signed
with its key.  We could verify against their key, but since the
reference client developers are currently unwilling to support other
implementations' alert messages, we will not relay theirs.

peer.go

@@ -1468,7 +1468,14 @@ out:
 			p.handlePongMsg(msg)
 
 		case *btcwire.MsgAlert:
-			p.server.BroadcastMessage(msg, p)
+			// Intentionally ignore alert messages.
+			//
+			// The reference client currently bans peers that send
+			// alerts not signed with its key.  We could verify
+			// against their key, but since the reference client
+			// is currently unwilling to support other
+			// implementions' alert messages, we will not relay
+			// theirs.
 
 		case *btcwire.MsgMemPool:
 			p.handleMemPoolMsg(msg)