A couple fixes to improve debugging of non-concrete models or model classes.
A couple fixes to improve debugging of non-concrete models or model classes.

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