+dnl Set the backup prefix
+undefine([backup-prefix])dnl
+AC_ARG_WITH([hash-backup],
+ [ --with-hash-backup use # as the backup prefix (default: ,)])
+if test x"$with_hash_backup" != x -a x"$with_hash_backup" != x"no"; then
+ backup_prefix="#"
+else
+ backup_prefix=","
+fi
+AC_DEFINE_UNQUOTED(BACKUP_PREFIX, "$backup_prefix")dnl
+