I've posted JIRA issue on the problem: https://jira.jboss.org/browse/JBAS-8361
I´ve had the same problem when I installed Richfaces 4 M4 and deployed it in JBoss 6 M5.
I've added the following WEB-INF/jboss-scanning.xml as well to solve the problem:
<scanning xmlns="urn:jboss:scanning:1.0">
<path name="WEB-INF/classes">
</path>
<path name="WEB-INF/lib/guava-r05.jar">
<exclude name="com.google.common.collect" />
</path>
</scanning>