fixed compound model slicing errors
fixed compound model slicing errors

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