simmer 4.4.2

• Fix memory issues in trap(), synchronize() and rollback(). These are
  stateful activities that require storing information about passing arrivals to
  manage clones or redirections. These activities were not properly cleaning
  their storage when arrivals were rejected at some point in the trajectory. As
  a result, certain simulations with these activities involved may show random
  improper behaviour depending on how memory reuse happens. This patch unifies
  storage management for stateful activities, adds a new interface to register
  these activities and another interface for arrivals to notify their
  termination, so that the stored information is properly cleaned up (#231).
• Fix state sharing in round-robin policy operation in select() (#233).