Fix missing format strings
From: Jari Aalto <jari.aalto@cante.net>

--- a/zooadd.c
+++ b/zooadd.c
@@ -542,7 +542,7 @@
          status = getfile (this_file, zoo_file, -1L, 1);
          if (status != 0) {  /* if III */
             success = 0;
-            printf (disk_full);
+            printf ("%s", disk_full);
             exit_status++;
          } else {
             success = 1;
