#8 Consider adding hooks to the backend for vm data

[Kevan Carstensen]

I'm attaching a patch that adds a couple of new functions to vSPCBackendMemory. notify_vm_msg is called when data is received from a VM to be written to listening clients with whatever is to be written to the clients, along with the uuid and name of the source VM. vm_msg_hook is a hook that is called with the arguments to notify_vm_msg. The new_vm_data method is also changed to call notify_vm_msg as appropriate. These modifications make it easy to create a logging backend using the external backend mechanism in vSPC while keeping the details of logging out of vSPC.py. Do you have any thoughts or concerns about this patch? Would you consider integrating it into vSPC.py?