anchor.diff:  
           let client = new HttpClient(handler)
           match auth with
  +        | None when not (isNull githubToken) ->
  +            client.DefaultRequestHeaders.Authorization <-
  +                new System.Net.Http.Headers.AuthenticationHeaderValue("token", githubToken)
           | None -> handler.ServerCredentials <- CredentialCache.DefaultCredentials
           | Some(Credentials({Username = username; Password = password; Type = AuthType.Basic})) ->
               // see lengthy comment below.
  
positive.code:         env = "true" || env = "yes" || env = "y"
  
  let createHttpClient (url,auth:Auth option) =
  #if !NO_WINCLIENTHANDLER
      if isWindows && not useDefaultHandler then
          // See https://github.com/dotnet/corefx/issues/31098
  
negative.code: 
          let client = new HttpClient(handler)
          match auth with
          | None when not (isNull githubToken) ->
              client.DefaultRequestHeaders.Authorization <-
                  new System.Net.Http.Headers.AuthenticationHeaderValue("token", githubToken)
          | None -> handler.UseDefaultCredentials <- true
          | Some(Credentials({Username = username; Password = password; Type = AuthType.Basic})) ->
              // http://stackoverflow.com/questions/16044313/webclient-httpwebrequest-with-basic-authentication-returns-404-not-found-for-v/26016919#26016919
  