Merge: Nit for mac

Some minor, but needed, tweaks to allow the compilation of Nit on Mac OS X

A special page is also created: http://nitlanguage.org/on_mac/

Currenlty, only 31 tests does not pass, most of them are platform or FFI related (some SDK are missing).

Pull-Request: #517
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc tests/tests.sh
Simple merge