adjust raco test so that it accepts multiple -s arguments on the command-line
adjust raco test so that it accepts multiple -s arguments on the command-line

This is, afaict, a completely backwards compatible way to add this
functionality in the sense that any of the non-error command-line
arguments passed to raco test before still do precisely the same
things

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket