Merge: More lazyness in standard

Make lazy some attributes of often used classes. So that the attribute creation cost only when they are really used.

More impact that initially imagined:

for nitc/nitc/nitc
before: 7.188
after: 7.008 (-2.5%)

Pull-Request: #1188
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

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