基于NS2（ns-2.1b8）的qos补丁

Overview of changes in qosrns-0.2-pre1 1. qosrns is implemented as a seperate module, so it can coexist with linkstate routing 2. qosrns uses RtModule interface, thus making it easy to use it with other routing modules 3. qosrns now supports on demand route computation. it is changed by setting variable Agent/QOSPF onDemand 4. qosrns now supports fine grained policy about when to send link updates. it could be send periodically, as well as when bandwidth changes by a certain percent. it can also use a hold down timer to not send updates too quickly. it is controoled by modifying following 3 variables: Agent/QOSPF set advertInterval #periodic update interval Agent/QOSPF set advertHoldDownInterval #hold down timer for updates Agent/QOSPF set advertMinBwChangePercent #updates due to bw changes are only sent when bw changes by this percent