Add cron script to prune thumbnail cache (close #2)

cron.php

@@ -0,0 +1,21 @@
+<?php
+
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+// Remove old thumbnails
+echo "Pruning thumbnail cache...\n";
+$path = __DIR__ . '/cache/thumb/';
+if ($handle = opendir($path)) {
+    while (false !== ($file = readdir($handle))) {
+        if ((time() - filectime($path . $file)) > 60 * 60 * 24) {
+            if (preg_match('/\.jpg$/i', $file)) {
+                echo "Deleting $file\n";
+                unlink($path . $file);
+            }
+        }
+    }
+}