Test implementation of deferred calculation of the 'get()' part of le…

[dimula73]

…nses

WARNING: this patch is only a proof of concept. It breaks a lot of unittests and I don't know how to fix them.

The perpose of this patch is twofold:

1. Avoid execution of the 'get()' part fo the lens when only set is requested
2. Avoid double expiring of the object when 'get()' part of the lens accepts the "whole" object as a non-reference