Backport unused dependency check to Python 2.6
Backport unused dependency check to Python 2.6

We support CentOS 6, which comes with Python 2.6.
Set literals were introduced in Python 2.7.

vmamidi/trafficserver,chenglongwei/trafficserver,reveller/trafficserver,rahmalik/trafficserver,rahmalik/trafficserver,davidbz/trafficserver,duke8253/trafficserver,dyrock/trafficserver,rahmalik/trafficserver,duke8253/trafficserver,reveller/trafficserver,pbchou/trafficserver,chenglongwei/trafficserver,pbchou/trafficserver,taoyunxing/trafficserver,rahmalik/trafficserver,chenglongwei/trafficserver,persiaAziz/trafficserver,bryancall/trafficserver,taoyunxing/trafficserver,clearswift/trafficserver,rpufky/trafficserver,bryancall/trafficserver,clearswift/trafficserver,persiaAziz/trafficserver,chenglongwei/trafficserver,rpufky/trafficserver,davidbz/trafficserver,dyrock/trafficserver,reveller/trafficserver,rpufky/trafficserver,clearswift/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,dyrock/trafficserver,PSUdaemon/trafficserver,clearswift/trafficserver,chitianhao/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,pbchou/trafficserver,chenglongwei/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,clearswift/trafficserver,dyrock/trafficserver,PSUdaemon/trafficserver,PSUdaemon/trafficserver,PSUdaemon/trafficserver,SolidWallOfCode/trafficserver,chenglongwei/trafficserver,persiaAziz/trafficserver,SolidWallOfCode/trafficserver,chitianhao/trafficserver,taoyunxing/trafficserver,duke8253/trafficserver,taoyunxing/trafficserver,rpufky/trafficserver,rpufky/trafficserver,bryancall/trafficserver,reveller/trafficserver,chitianhao/trafficserver,persiaAziz/trafficserver,bryancall/trafficserver,reveller/trafficserver,persiaAziz/trafficserver,chitianhao/trafficserver,SolidWallOfCode/trafficserver,persiaAziz/trafficserver,duke8253/trafficserver,dyrock/trafficserver,PSUdaemon/trafficserver,PSUdaemon/trafficserver,davidbz/trafficserver,pbchou/trafficserver,rahmalik/trafficserver,davidbz/trafficserver,rpufky/trafficserver,vmamidi/trafficserver,PSUdaemon/trafficserver,persiaAziz/trafficserver,vmamidi/trafficserver,reveller/trafficserver,chitianhao/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,chenglongwei/trafficserver,rahmalik/trafficserver,taoyunxing/trafficserver,bryancall/trafficserver,clearswift/trafficserver,taoyunxing/trafficserver,dyrock/trafficserver,rpufky/trafficserver,reveller/trafficserver,taoyunxing/trafficserver,reveller/trafficserver,rahmalik/trafficserver,duke8253/trafficserver,reveller/trafficserver,taoyunxing/trafficserver,clearswift/trafficserver,PSUdaemon/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,clearswift/trafficserver,chenglongwei/trafficserver,rpufky/trafficserver,dyrock/trafficserver,clearswift/trafficserver,rpufky/trafficserver,davidbz/trafficserver,vmamidi/trafficserver,PSUdaemon/trafficserver,rahmalik/trafficserver,bryancall/trafficserver,persiaAziz/trafficserver,taoyunxing/trafficserver,rahmalik/trafficserver,chitianhao/trafficserver