message: Allow unused variable in sprs-benches
  This unused variable is actually used with the eigen feature on, but I
  keep it present witht the warning deactivated because handling its
  disappearance in the rest of the code would cause too much hassle.
diff: @@ -83,6 +83,7 @@ fn eigen_prod(a: sprs::CsMatView<f64>, b: sprs::CsMatView<f64>) -> usize {
  struct BenchSpec {
  shape: (usize, usize),
  densities: Vec<f64>,
  + #[allow(dead_code)] // this variable is only present with eigen's feature
  forbid_eigen: bool,
  shapes: Vec<(usize, usize)>, // will trigger shape benchmark
  nnz_over_rows: usize, // used to compute density in shape benchmark
  