implemented d_xyz attribute on CartesianDifferential
implemented d_xyz attribute on CartesianDifferential

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