added validators for mask and error
added validators for mask and error

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