error if maxval != 255 in read-{pgm/ppm}-file
error if maxval != 255 in read-{pgm/ppm}-file


wkentaro/EusLisp,aginika/EusLisp,bmagyar/EusLisp,aginika/EusLisp,bmagyar/EusLisp,aginika/EusLisp,aginika/EusLisp,wkentaro/EusLisp,bmagyar/EusLisp,wkentaro/EusLisp,bmagyar/EusLisp,wkentaro/EusLisp