loosen the check in get_deriv_key to look in compatible_differentials
loosen the check in get_deriv_key to look in compatible_differentials

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