Keep Cross._ids in sync with Cross._cache
Keep Cross._ids in sync with Cross._cache

Without this fix, input objects that are re-added after being removed were not re-crossed.
nyurik/vega,uwdata/vega,seyfert/vega,vega/vega,timelyportfolio/vega,seyfert/vega,nyurik/vega,nyurik/vega,seyfert/vega,vega/vega,timelyportfolio/vega,vega/vega,uwdata/vega,vega/vega,lgrammel/vega