Merge: Kill oldstyle attributes

Remove remaining usage of old style attributes declarations `var _foo`.

Also remove the annotation `old_style_init` in the parser.

Pull-Request: #712
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc src/astvalidation.nit
Simple merge