This patch add the threshold feature (and configuration
option) as described in "From a Trickle to a Flood:
Active Attacks on Several Mix Types"
to improve the minimum anonymity.
Now RATE operates on all messages minus the POOLSIZE
and not on all messages present in the pool. Also a
sanity check in RATE option is maked and the default
value is changed to 90 (from 95). It should be smaller
NOTE: I don't have all the current CVS tree, then i
can't test it.