Ignore deprecated values

[SkySkimmer]

I found this useful when trying to run the analyser on coq/coq.

[alainfrisch]

I can see cases where this is useful, but I think this should be controlled by some command-line flag. One might want to mark some function as being deprecated within a project, incrementally get rid of it, but then finally actually remove the function : in such a scenario, one want the analyzer to report such function even if deprecated.