fixes #479, fallback on srand.php to generate random bytes

when random_compat does not find a suitable random generator.

srand.php comes from https://github.com/GeorgeArgyros/Secure-random-bytes-in-PHP

include/functions_session.inc.php

@@ -64,11 +64,21 @@ function generate_key($size)
 {
   include_once(PHPWG_ROOT_PATH.'include/random_compat/random.php');
 
+  try
+  {
+    $bytes = random_bytes($size+10);
+  }
+  catch (Exception $ex)
+  {
+    include_once(PHPWG_ROOT_PATH.'include/srand.php');
+    $bytes = secure_random_bytes($size+10);
+  }
+
   return substr(
     str_replace(
       array('+', '/'),
       '',
-      base64_encode(random_bytes($size+10))
+      base64_encode($bytes)
       ),
     0,
     $size