Merge: Regular Expression fix with Unicode

Fixes issue #1659, RE are now a bit more expensive, but they should behave correctly when dealing with Unicode Strings.

Pull-Request: #1662
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --cc lib/core/re.nit
Simple merge

diff --cc lib/core/text/flat.nit
Simple merge

diff --cc lib/core/text/native.nit
Simple merge