Port the code to PHP 8.5.

Replace the short open tags and the removed functions (mcrypt, mysql_error,
salt-less crypt). Decode the reCAPTCHA reply as JSON, turn off mysqli
exceptions, drop stripslashes(), and default missing input values.
Fix the misplaced continue in prune_images().

publish/logout.php

@@ -1,4 +1,4 @@
-<?
+<?php
 //include_once('../session.lib.php');
 header( 'Cache-Control: no-store, no-cache, must-revalidate' );
 header( 'Cache-Control: post-check=0, pre-check=0', false );