Add functionality to lookup an object and lock it. Additional the case is
handled that a object may be already in-destruction and the lookup will deny
returning the object.
The object_pool generalize the lookup and lock functionality of the rpc_server
and serve as base for following up patches to fix dangling pointer issues.
With this patch GDB monitor provides a 'config' file to the target. Its
content can be defined in the <config> sub node of the <target> XML node.
Fixes#179.
