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Don't try to be clever in update by checking if the value is equal to the default, it makes everything complicted. Update should just update. If we want something incremental we can do it trivially in the client: just do a get(), complete, then set().

- now OK to communicate with several clients at once, over different sockets (unique socket name/ip port is
  created automatically)
- started to replace old ConnectionManager infrastructure with onelab (already ok with "gmsh -listen")