+file. Abandon key exchanges when a bad packet is received. Modify
+protocol to include version fields, as described in the NOTES
+file. Implement keepalive mode. Make policy about when to initiate key
+exchanges more configurable (how many NAKs / bad reverse-transforms
+does it take to prompt a key exchange?)
+
+slip.c: restart userv-ipif to cope with soft routes? Restart it if it
+fails in use?
+
+transform.c: separate the transforms into multiple parts, which can
+then be combined in the configuration file. Will allow the user to
+plug in different block ciphers, invent an authenticity-only mode,
+etc.