output->_display_cache() optimization

faster method to remove the timestamp from the content to be served
diff --git a/system/core/Output.php b/system/core/Output.php
index 5ec8c4b..2bf4e99 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -575,7 +575,7 @@
 		}
 
 		// Display the cache
-		$this->_display(str_replace($match[0], '', $cache));
+		$this->_display(substr($cache, strlen($match[0])));
 		log_message('debug', 'Cache file is current. Sending it to browser.');
 		return TRUE;
 	}