Merge: Benchs nullables

Allow us to compare engine performances with or without isset-checks before non-nullable attribute accesses

Pull-Request: #419
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc src/abstract_compiler.nit
Simple merge

diff --cc src/separate_compiler.nit
Simple merge