Merge: Arrays comprehension

Implements and closes #896

Was not as hard as expected, not bad for less than 12 hours of thinking, coding and sleeping.

Pull-Request: #1042
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>

diff --cc src/compiler/abstract_compiler.nit
Simple merge