Bug 16229: Deep copy on first L2 fetch

Bug 16229: Deep copy on first L2 fetch

When a value exists in L2 cache but not in L1 cache, it should be deep
copied if needed (i.e. not a scalar). Otherwise the calling code is able
to modify the value in cache.
Note that is theoretical, it's possible that no code does that.

Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>
Signed-off-by: Brendan Gallagher <bredan@bywatersolutions.com>
(cherry picked from commit 956dc953b52a1fd525bc75682bbdfe6848683ace)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>