anchor.diff:  
           let refs =
             project.References
  -          |> Seq.choose Project.getAssemblyLocation
  +          |> Seq.collect Project.getAssemblyLocations
             |> Seq.append portableRefs
             |> Seq.toList
   
  
positive.code: 
        let getPortableReferences (project: DotNetProject) configSelector =
            project.References
            |> Seq.choose getAssemblyLocation
            |> Seq.append (portableReferences project)
            |> set
            |> Set.toList
  
negative.code:            match referencedAssemblies |> Seq.tryFind Project.isPortable with
             | Some _ -> true
             | None -> project.References
                       |> Seq.filter (fun r -> r.ReferenceType = ReferenceType.Assembly)
                       |> Seq.collect Project.getAssemblyLocations
                       |> Seq.tryFind isAssemblyPortable
                       |> Option.isSome
  
  