Fixes project menu with lablgtk3

See merge request frama-c/frama-c!2270

incidentally, this avoids having the phantom duplication of current project
when duplicating a non-current project.

[Gui] Printer_tag: removes the cache for the printer.

See merge request frama-c/frama-c!2269

Fixes a bug in the GUI where function contracts disappeared when the
preconditions were unfold at a call site.

Fix/virgile/why3 conf

See merge request frama-c/frama-c!2264

[rte] Do not visit variable declarations; fixes a crash.

See merge request frama-c/frama-c!2261

Also use FC's Makefile standard variables whenever possible

See merge request frama-c/frama-c!2262

Merge branch '650-erreur-lors-de-la-generation-des-fichiers-why3-avec-certaines-construction-pas-encore-vraiment-identifie' into 'stable/potassium'

Resolve "Erreur lors de la génération des fichiers Why3 avec certaines construction (pas encore vraiment identifié)"

See merge request frama-c/frama-c!2258