bare return should not default to slip
bare return should not default to slip

Added tests to make sure bare return yields Nil, and that explicit
Slip/Empty returns do correctly interpolate nothing into lists.
(RT #126049 rejected)

dankogai/roast,skids/roast,zostay/roast,dogbert17/roast,bitrauser/roast,skids/roast,cygx/roast,cygx/roast,dankogai/roast,zostay/roast,dankogai/roast,perl6/roast,cygx/roast,dogbert17/roast,zostay/roast,b2gills/roast,skids/roast,bitrauser/roast,b2gills/roast,b2gills/roast