As an alternative to #3929, create copies of BaseColumn and subclasses on an as-needed basis when using those columns to store multi-dimensional data.  The new classes have the slower __getitem__ implementation, while the stock classes go straight through ndarray.__getitem__ and retain its performance.
As an alternative to #3929, create copies of BaseColumn and subclasses on an as-needed basis when using those columns to store multi-dimensional data.  The new classes have the slower __getitem__ implementation, while the stock classes go straight through ndarray.__getitem__ and retain its performance.

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