The original pool on machine is Topology::Local::masterPool(), avalibalbe
only as const reference, also available through Topology::Mpi::masterPool()
and Parallel::masterPool().

All pools should be descendants of this one.

Espetially because it got queued on remote MPI workers who cannot dereference
the Handle.

If handle is remote, it cannot be dereferenced and extension must
therefore access node stored alongside in Vertex.
Also it is no longer possible to detect owner of Handle. It can only be
detected if Handle belongs to this worker (Store::knows).

Store must be explicitly added to remote vertices and they must be explicitly
deleted in visitor.

Also seprate call to becomeMaster() is no longer needed.

To be used by to specify MPI ranks.

Since we use char *dereference of ValueRefs for the purpose of bound checking,
we need to be able to handle the cases where the ValueRef points inside a valid
range, even though it doesn't fit entirely. This is not really a problem, since
all (potentially dangerous) dereferences need to be guarded by a bounds check
anyway.