Undeprecate normfro

Cf. Alan's comment, https://github.com/JuliaLang/julia/pull/6057#issuecomment-50057813, to which I agree. See also [the list](https://groups.google.com/forum/#!searchin/julia-users/normfro/julia-users/RJO-JCVV7rg/Mviek4LxWqQJ).