fix sorting with multi-key columns
fix sorting with multi-key columns

fixes #23

codeaudit/spree,codeaudit/spree,cafreeman/spree,nkhuyu/spree,hammerlab/spree,cafreeman/spree,hammerlab/spree,nkhuyu/spree,cafreeman/spree,hammerlab/spree,nkhuyu/spree,codeaudit/spree