RegionFactory.stop does not undefine pending-puts cache

When shutting down the RegionFactory the caches belonging to regions are cleaned up; pending-puts caches are not, though.

Actually this is not really a problem since SessionFactoryImp.close > EnabledCaching.close iterates through all regions and calls 'destroy'. However we should centralize the shutdown a bit and make the impl more resilient against starting with existing configuration.