added constants.php file and implemented constants for file system modes
diff --git a/system/libraries/Log.php b/system/libraries/Log.php
index f9ca85a..1aa8bd0 100644
--- a/system/libraries/Log.php
+++ b/system/libraries/Log.php
@@ -109,7 +109,7 @@
 		flock($fp, LOCK_UN);

 		fclose($fp);

 	

-		@chmod($filepath, 0666); 		

+		@chmod($filepath, FILE_WRITE_MODE); 		

 		return TRUE;

 	}