Set the session parameter HTTP_INVOKER_CLASS to "org.apache.chemistry.opencmis.client.bindings.spi.http.ApacheClientHttpInvoker" and make sure that you have the Apache HTTP Client jars (tested with 4.2.5) in your classpath.
For more session parameters see: http://chemistry.apache.org/java/0.10.0/maven/apidocs/org/apache/chemistry/opencmis/commons/SessionParameter.html