Fix documentation build -- astropy.io.vo was failing to import (in the docbuild context only) due to an inadvertent cyclical import.
Fix documentation build -- astropy.io.vo was failing to import (in the docbuild context only) due to an inadvertent cyclical import.

DougBurke/astropy,saimn/astropy,lpsinger/astropy,kelle/astropy,kelle/astropy,mhvk/astropy,kelle/astropy,pllim/astropy,mhvk/astropy,StuartLittlefair/astropy,mhvk/astropy,lpsinger/astropy,AustereCuriosity/astropy,DougBurke/astropy,DougBurke/astropy,pllim/astropy,saimn/astropy,MSeifert04/astropy,funbaker/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,dhomeier/astropy,lpsinger/astropy,MSeifert04/astropy,astropy/astropy,mhvk/astropy,dhomeier/astropy,bsipocz/astropy,MSeifert04/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,astropy/astropy,larrybradley/astropy,stargaser/astropy,StuartLittlefair/astropy,funbaker/astropy,joergdietrich/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,StuartLittlefair/astropy,bsipocz/astropy,StuartLittlefair/astropy,mhvk/astropy,StuartLittlefair/astropy,funbaker/astropy,pllim/astropy,astropy/astropy,kelle/astropy,MSeifert04/astropy,AustereCuriosity/astropy,dhomeier/astropy,joergdietrich/astropy,joergdietrich/astropy,bsipocz/astropy,tbabej/astropy,kelle/astropy,joergdietrich/astropy,stargaser/astropy,tbabej/astropy,AustereCuriosity/astropy,bsipocz/astropy,astropy/astropy,saimn/astropy,DougBurke/astropy,saimn/astropy,joergdietrich/astropy,astropy/astropy,AustereCuriosity/astropy,stargaser/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,tbabej/astropy,tbabej/astropy,funbaker/astropy,lpsinger/astropy,AustereCuriosity/astropy,pllim/astropy,saimn/astropy,stargaser/astropy,larrybradley/astropy,dhomeier/astropy,pllim/astropy,dhomeier/astropy,tbabej/astropy