Merge: Text attribute accesses optimization

As a small optimization, accesses to private attributes in Text are replaced by direct accesses as in `file` or `collection`.

On the compiler this yields between 3 and 4% improvement in performances, however in some programs like nitmd, this yields around 15% optimization.

Pull-Request: #1683
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>