increased randomness of file name used in is_really_writable()
diff --git a/system/codeigniter/Common.php b/system/codeigniter/Common.php
index eb9dce6..73ff019 100644
--- a/system/codeigniter/Common.php
+++ b/system/codeigniter/Common.php
@@ -62,7 +62,7 @@
 	// write a file then read it.  Bah...
 	if (is_dir($file))
 	{
-		$file = rtrim($file, '/').'/'.md5(rand(1,100));
+		$file = rtrim($file, '/').'/'.md5(mt_rand(1,100).mt_rand(1,100));
 
 		if (($fp = @fopen($file, FOPEN_WRITE_CREATE)) === FALSE)
 		{