code: public function getMessages ($channelId, $limit = 20, $since = null, $before = null)
  	{
  		$profiler = Neuron_Profiler_Profiler::getInstance ();
  
  		if (isset ($since))
  		{
  			// Here we do some magic to check if the last id has changed
  			$cName = $this->sPrefix . 'lastmessage_' . $channelId;
  
  			$profiler->message ('Checking ' . $cName . ' against ' . $since);
  
  			if (
  				$this->objCache->hasCache ($cName)
  				&& $this->objCache->getCache ($cName) <= $since
  			) {
  				$profiler->message ('Not checking for new messages');
  				return array ();
  			}
  		}
  
  		$profiler->message ('Checking for new messages');
  		return parent::getMessages ($channelId, $limit, $since, $before);
  	}
docs: Return the latest messages since $since.
  $since should be the last received message ID.