check for single value expressions in ensure_single_value
check for single value expressions in ensure_single_value

Only wrap the argument when the optimizer is not sure that
it is a single valued expression. This allows to remove the
checks in the calling sites.

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