teach find_root_device to deal with /dev/ subdirs

(by "Kirill K. Smirnov" <lich@math.spbu.ru>)

coreutils/rm.c

@@ -40,7 +40,7 @@ int rm_main(int argc, char **argv)
 		do {
 			const char *base = bb_get_last_path_component(*argv);
 
-			if ((base[0] == '.') && (!base[1] || ((base[1] == '.') && !base[2]))) {
+			if (DOT_OR_DOTDOT(base)) {
 				bb_error_msg("cannot remove '.' or '..'");
 			} else if (remove_file(*argv, flags) >= 0) {
 				continue;