message: Show registry name in messages if possible
  This fixes most messages to display registry names instead of URLs.
diff: @@ -216,9 +216,9 @@ impl SourceId {
  pub fn display_index(self) -> String {
  if self.is_default_registry() {
  - "crates.io index".to_string()
  + format!("{} index", CRATES_IO_DOMAIN)
  } else {
  - format!("`{}` index", url_display(self.url()))
  + format!("`{}` index", self.display_registry_name())
  }
  }
  @@ -463,7 +463,7 @@ impl fmt::Display for SourceId {
  Ok(())
  }
  SourceKind::Path => write!(f, "{}", url_display(&self.inner.url)),
  - SourceKind::Registry => write!(f, "registry `{}`", url_display(&self.inner.url)),
  + SourceKind::Registry => write!(f, "registry `{}`", self.display_registry_name()),
  SourceKind::LocalRegistry => write!(f, "registry `{}`", url_display(&self.inner.url)),
  SourceKind::Directory => write!(f, "dir {}", url_display(&self.inner.url)),
  }
  