ease the migration process for the previous security patch (by introducing another migration); restore php 5.4 compatibility (introducing a polyfill system)

inc/polyfill.php

@@ -0,0 +1,28 @@
+<?php
+
+// PHP 5.4
+
+if (!function_exists('hex2bin')) {
+	function hex2bin($data) {
+		return pack("H*" , $hex_string);
+	}
+}
+
+// PHP 5.6
+
+if (!function_exists('hash_equals')) {
+	function hash_equals($ours, $theirs) {
+		$ours = (string)$ours;
+		$theirs = (string)$theirs;
+
+		$tlen = strlen($theirs);
+		$olen = strlen($ours);
+
+		$answer = 0;
+		for ($i = 0; $i < $tlen; $i++) {
+			$answer |= ord($ours[$olen > $i ? $i : 0]) ^ ord($theirs[$i]);
+		}
+
+		return $answer === 0 && $olen === $tlen;
+	}
+}