Add an option to genode.core.children and genode.init.children
for specifying a Nic driver for the exclusive use of the child
for which it is added. This mechanism is to support the nic_router
but it is reusable for arbitrary children.
Retrieve ROMs in the common case by full store path. This reduces
the need for route policies for driving relative requests into
absolute package paths.
Making library requests by absolute path required libraries to be
stored in the core image as such, and it follows that program
binaries should be handled in the same way. This makes requests
to core and to a file-system store more consistent, and makes
dependency detection more robust.