This changeset attempts to breach into the implementation design of OutputSlot
(while largely retaining the API and the »Output Slot Protocol«).
While the actual problem that brought me to this point can be traced back to some
rather obvious mistake, namely to conflate the `BufferProvider` used as
backing implementation with a `BufferProvider` used as front-end API,
creating the new connections to use an `OutputBufferProxy` unveils some
further long-standing structural mismatch; notably this leads to the
difficulties to get the lifecylce management of `OutputSlot` and `DataSink`
under control.
So I remove one entire level from the implementation,
in a bold move to realign the design with the prospective usage pattern.
Obviously, this breaks a lot of further code, and I need to rewire
the Allocation implementation altogether, and provide a new functor based
implementation for `DataSink`
Ichthyostega
473299fb5a