Register buffers with an execution context.

template<
    typename ExecutionContext,
    typename MutableBufferSequence,
    typename Allocator>
buffer_registration< MutableBufferSequence, Allocator > register_buffers(
    ExecutionContext & ctx,
    const MutableBufferSequence & buffer_sequence,
    const Allocator & alloc,
    typename constraint< is_convertible< ExecutionContext &, execution_context & >::value >::type  = 0);