Change behavior of HDU lookup by name to not iterate over all HDUs in a needless search for duplicates.  This behavior was previously not tested for anyways, and is somewhat user-hostile anyways.
Change behavior of HDU lookup by name to not iterate over all HDUs in a needless search for duplicates.  This behavior was previously not tested for anyways, and is somewhat user-hostile anyways.

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