Add a warning shown on "opam update" to inform users who are using an out-of-date opam binary
Add a warning shown on "opam update" to inform users who are using an out-of-date opam binary

nberth/opam-repository,codinuum/opam-repository,pqwy/opam-repository,pirbo/opam-repository,pirbo/opam-repository,jhwoodyatt/opam-repository,Leonidas-from-XIV/opam-repository,ocaml/opam-repository,codinuum/opam-repository,pqwy/opam-repository,Leonidas-from-XIV/opam-repository,jhwoodyatt/opam-repository,fpottier/opam-repository,ocaml/opam-repository,fpottier/opam-repository,nberth/opam-repository