Ensure that Seam enable restlets close temporary CoreSession instances they create

Most restlet implementations provided by default assume that they are run in a given conversation context that might allow them to reuse documentManager. If documentManager is not available, the create it and don't bother to close the session afterward.

Instead they should:

• try to reuse any documentManager instance available from the context if it matches the requested repo
• if not, create a temporary CoreSession instance independantly of the Seam stateful contexts and take care to close it in a finally block as usual