epoch_append should be called at the point the object is not reachable
anymore, otherwise a thread from a "future" might still access it post
reclamation.
Similar to the algorithm presented in
https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-579.pdf
Not completely lock-free at the moment. Also the problems with epoch
based memory reclamation are still present - a thread actively observing
an epoch getting stuck will prevent LloadConnections and LloadOperations
being freed, potentially running out of memory.
