message: Fix TODO about nightly features
diff: @@ -276,6 +276,7 @@ macro_rules! features {
  pub struct Features {
  $($feature: bool,)*
  activated: Vec<String>,
  + nightly_features_allowed: bool,
  }
  impl Feature {
  @@ -416,6 +417,7 @@ impl Features {
  ret.add(feature, config, warnings)?;
  ret.activated.push(feature.to_string());
  }
  + ret.nightly_features_allowed = config.nightly_features_allowed;
  Ok(ret)
  }
  @@ -497,9 +499,7 @@ impl Features {
  let feature = feature.name.replace("_", "-");
  let mut msg = format!("feature `{}` is required", feature);
  - // TODO
  - let channel = channel();
  - if channel == "nightly" || channel == "dev" {
  + if self.nightly_features_allowed {
  let s = format!(
  "\n\nconsider adding `cargo-features = [\"{0}\"]` \
  to the manifest",
  