fix expt on negative powers of -inf.0 and +inf.0
fix expt on negative powers of -inf.0 and +inf.0

svn: r2355

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