Handle doctest warning in unified IO [docs only]
Handle doctest warning in unified IO [docs only]

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