more entropy on session id

all tests passing

src/Ratchet/Wamp/WampConnection.php

@@ -17,7 +17,7 @@ class WampConnection extends AbstractConnectionDecorator {
         parent::__construct($conn);
 
         $this->WAMP            = new \StdClass;
-        $this->WAMP->sessionId = uniqid();
+        $this->WAMP->sessionId = md5(uniqid(mt_rand(), true));
         $this->WAMP->prefixes  = array();
 
         $this->send(json_encode(array(WAMP::MSG_WELCOME, $this->WAMP->sessionId, 1, \Ratchet\VERSION)));

tests/unit/Wamp/TopicTest.php

@@ -81,7 +81,7 @@ class TopicTest extends \PHPUnit_Framework_TestCase {
         $topic->add($first);
         $topic->add($second);
         $topic->add($third);
-
+        
         $topic->broadcast($msg, array($second->WAMP->sessionId));
     }