Improve diagnostic messages on module failure
Improve diagnostic messages on module failure

If a module fails to load, a stack trace is now printed under most
conditions.

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