Refactor to use modified TCP timestamps as selective acks, works without losses
Version that kind of works with losses. Need to handle lost retransmissions.

Conflicts:
	tcp/tcp-rational.cc
First cut of retransmission timer, doesn't retransmit several packets
Throw in asserts for good measure.
Distinguish total ack samples from in order samples.
ns-2 and everyone else seems to use 200 ms as the minrto!
Can't assert because the base class has other timers as well.