boot: restore setting stack size, and remove wrong experimental

#ifndef DOS that shouldn't have been committed.

boot/bootimage.c

@@ -767,10 +767,8 @@ char *select_image(char *image)
 	ino_t image_ino;
 	struct stat st;
 
-#ifndef DOS
 	image= strcpy(malloc((strlen(image) + 1 + NAME_MAX + 1)
 						 * sizeof(char)), image);
-#endif
 
 	fsok= r_super(&block_size) != 0;
 	if (!fsok || (image_ino= r_lookup(ROOT_INO, image)) == 0) {