848832f8b0
Since 44610c787 RCU keeps references until another write happens.
even before then, some shared_ptr references may have been kept.
When using a process graph, a route's activision-set can
hold references to other graph-nodes (routes). This lead
to Routes not being deleted until a second graph-reorder
flushed the RCU.
Please see the Ardour web site at https://ardour.org/ for all documentation..
For information on building ardour:
https://ardour.org/development.html