[PATCH] [WIP] Large refactoring of AST/APValue

[Gautier DI FOLCO]

  I agree on the fact that the layering is incorrect, that what I was figuring out before submit this proposition. Maybe some kind of inheritance will be more relevent here (I have seen that some class are "duplicated").

  The evolutivity is not my main concern here, see all the dependencies of an element is more important, this will allow to act from the chief party concerned and do simplier things by removing the noise generated by accessors.

http://llvm-reviews.chandlerc.com/D3091