revent: Allow True as shorthand for event halting
revent: Allow True as shorthand for event halting

If a handler returns True, it now halts the event.  Some other minor tweaks
in there as well.

jacobq/csci5221-viro-project,adusia/pox,kulawczukmarcin/mypox,diogommartins/pox,kulawczukmarcin/mypox,waltznetworks/pox,PrincetonUniversity/pox,jacobq/csci5221-viro-project,xAKLx/pox,denovogroup/pox,denovogroup/pox,kpengboy/pox-exercise,MurphyMc/pox,pthien92/sdn,pthien92/sdn,PrincetonUniversity/pox,kavitshah8/SDNDeveloper,VamsikrishnaNallabothu/pox,andiwundsam/_of_normalize,kavitshah8/SDNDeveloper,MurphyMc/pox,diogommartins/pox,chenyuntc/pox,chenyuntc/pox,jacobq/csci5221-viro-project,noxrepo/pox,denovogroup/pox,MurphyMc/pox,kpengboy/pox-exercise,jacobq/csci5221-viro-project,diogommartins/pox,waltznetworks/pox,adusia/pox,carlye566/IoT-POX,andiwundsam/_of_normalize,adusia/pox,diogommartins/pox,chenyuntc/pox,kavitshah8/SDNDeveloper,waltznetworks/pox,MurphyMc/pox,carlye566/IoT-POX,PrincetonUniversity/pox,noxrepo/pox,kulawczukmarcin/mypox,MurphyMc/pox,waltznetworks/pox,chenyuntc/pox,adusia/pox,carlye566/IoT-POX,carlye566/IoT-POX,PrincetonUniversity/pox,waltznetworks/pox,diogommartins/pox,VamsikrishnaNallabothu/pox,VamsikrishnaNallabothu/pox,adusia/pox,VamsikrishnaNallabothu/pox,kpengboy/pox-exercise,PrincetonUniversity/pox,xAKLx/pox,andiwundsam/_of_normalize,kpengboy/pox-exercise,denovogroup/pox,pthien92/sdn,VamsikrishnaNallabothu/pox,xAKLx/pox,xAKLx/pox,noxrepo/pox,xAKLx/pox,andiwundsam/_of_normalize,jacobq/csci5221-viro-project,carlye566/IoT-POX,pthien92/sdn,kulawczukmarcin/mypox,kulawczukmarcin/mypox,kavitshah8/SDNDeveloper,noxrepo/pox,chenyuntc/pox,denovogroup/pox,pthien92/sdn,kpengboy/pox-exercise