fix traverse_postorder
fix traverse_postorder

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