Hello,
as far as I can see, Alfresco 5.0 no longer ships with OpenCMIS client JARs. They were part of Alfresco 4.2.x but to my knowledge weren't used anywhere, which may be the reason they were removed in an effort to trim down the size of the web application.
So basically you need to make sure that you yourself deploy / bundle the necessary libraries into the web application.
EDIT: Correction - they no longer maintain that many libraries in their SVN which is why I did not find it, but the client JARs are still bundled with the web application (cross-checked with my 5.0 install).
You DO know that Alfresco has removed its JSF client Explorer with Alfresco 5.0.b? You may be in for an unpleasant surprise if you develop new functionality upon JSF unless you are building a completely custom UI that is already separate from Explorer.
Regards
Axel