Merge: lib/math: Added bin_not function to Int

Added missing function bin_not to `Int` as I might need it in the near future.

I figured it could be needed by someone else, so why not !

Pull-Request: #806
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc lib/standard/math.nit
Simple merge

diff --cc src/interpreter/naive_interpreter.nit
Simple merge