added masked array tests to nddata
added masked array tests to nddata

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