added hash_equals polyfill for old PHP versions

qa-include/qa-base.php

@@ -203,6 +203,20 @@
 			require_once QA_INCLUDE_DIR.'vendor/password_compat.php';
 		}
 
+		// http://php.net/manual/en/function.hash-equals.php#115635
+		if(!function_exists('hash_equals')) {
+			function hash_equals($str1, $str2) {
+				if(strlen($str1) != strlen($str2)) {
+					return false;
+				} else {
+					$res = $str1 ^ $str2;
+					$ret = 0;
+					for($i = strlen($res) - 1; $i >= 0; $i--) $ret |= ord($res[$i]);
+					return !$ret;
+				}
+			}
+		}
+
 		// http://stackoverflow.com/a/18277167
 		function ipv6_numeric($ip) {
 			$binNum = '';