fix traverse_postorder, delete commented code
fix traverse_postorder, delete commented code

aleksandr-bakanov/astropy,dhomeier/astropy,lpsinger/astropy,astropy/astropy,aleksandr-bakanov/astropy,astropy/astropy,lpsinger/astropy,saimn/astropy,mhvk/astropy,dhomeier/astropy,mhvk/astropy,astropy/astropy,StuartLittlefair/astropy,larrybradley/astropy,pllim/astropy,astropy/astropy,stargaser/astropy,saimn/astropy,dhomeier/astropy,MSeifert04/astropy,stargaser/astropy,stargaser/astropy,astropy/astropy,bsipocz/astropy,pllim/astropy,StuartLittlefair/astropy,pllim/astropy,lpsinger/astropy,lpsinger/astropy,MSeifert04/astropy,larrybradley/astropy,bsipocz/astropy,larrybradley/astropy,mhvk/astropy,larrybradley/astropy,bsipocz/astropy,saimn/astropy,saimn/astropy,MSeifert04/astropy,StuartLittlefair/astropy,saimn/astropy,dhomeier/astropy,StuartLittlefair/astropy,mhvk/astropy,bsipocz/astropy,StuartLittlefair/astropy,MSeifert04/astropy,stargaser/astropy,larrybradley/astropy,pllim/astropy,pllim/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,mhvk/astropy,aleksandr-bakanov/astropy,lpsinger/astropy