DTN2 TODO LIST
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- bundle status reports:
  - test with fragments

- dtndump utility

- forwarding logic
  - add transmission log
  - fix up bundle deletion before expiration time
  - honor bundle priority bits in forwarding
  - custody transfer
  - add bundle delete command
  - change the consumer_bundle to have a bit indicating whether or not
    fragments can be sent to it. if not, enqueue on the reassembler
    which should simply post a new event when the reassembly is
    completed.
  - bundle overwrite option
  - bundle echo option

- registrations
  - present / not present flag

- bundle protocol 
  - handle extension headers
  - change lengths to 64 bit (requires changing oasys serialize layer)

- misc
  - in tcl layer, add procs s.t. 'module var val' is interpreted as 
    'module set var val'
  - file-based backing store
  - control / management interface
  - simulator 'at' command