Added function to namespace which checks if namespace is empty

Hi,
First of all ... thanks a lot for this wonderful project.
We use this in our project to emit real time data. 
I'm adding a function to the Namespace class. We use this function a lot while creating/deleting dynamic namespaces. 
Its a small change but is quicker than getting the iterator to allClients and then counting the number of items.


Regards,
Chandrahaas