CometD demo on JBoss 6 - jboss6.x

Question

I am planning to use Cometd library in my application that runs on JBoss AS 6. Therefore I downloaded cometd 2.4.0 and tried to deploy example war (from cometd-demo/target) to my AS. I was aware that this was not possible without modifications, so I did the changes in web.xml:
Changed to servlet 3.0 in web-app tag (it is originally 2.5). Used complete tag from CometD faq answer. Also uncommented continuation filter that was already in web.xml, based on this description
Based on faq answer, added async-supported tag. However, this causes problems: if I just uncomment it, web.xml can't be parsed. I found out that this is due to order of tags in XML, so moved async-supported tag down the order, just after load-on-startup tag. However, Jboss still throws exceptions:
ERROR
[org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/cometd-demo-2.4.0].[cometd]]
Servlet.service() for servlet cometd threw exception:
java.lang.IllegalStateException: The servlet or filters that are being
used by this request do not support async operation
ERROR
[org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/cometd-demo-2.4.0].[cometd]]
Servlet.service() for servlet cometd threw exception:
java.lang.ClassNotFoundException:
org.eclipse.jetty.server.AbstractHttpConnection from
BaseClassLoader#12a54b
Complete web.xml file that I use is here.
Example runs no my Jboss despite all errors reported, but by watching firebug, I can see that it does quick pooling instead of long pool. It seems that server thinks that browser has multiple connections open, which is not the case (see JSON below):
[{"id":"137","successful":true,"advice":{"interval":2000,"reconnect":"retry","multiple-clients":true,"timeout":20000},"channel":"/meta/connect"}]
Did anyone managed to make examples work with JBoss as6 and how? What I did wrong here?

Answer 1

remove:
<!-- Portability Filter, needed only to run on non Jetty or non Servlet-3.0 containers -->
<filter>
<filter-name>continuation</filter-name>
<filter-class>org.eclipse.jetty.continuation.ContinuationFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>continuation</filter-name>
<url-pattern>/cometd/*</url-pattern>
</filter-mapping>
from web.xml

Answer 2

I have the same setup and the same problem even if I remove continuation filter from web.xml.
I've found a thread on cometd-users group complaining about multiple-client issue on Tomcat 7 and the cause seems to be a Tomcat bug around Content-Type that is not set to "application/json".
However I've inspected packets and on JBossAS6 the content-type is correctly set on server responses.
UPDATE
I've give a try using Jetty 7 and the problem disappeared. The "multiple-clients" issue affects Tomcat as well as JBoss6 AS