message: test to ensure triplet mats can be buit with non-usize index type
diff: @@ -466,12 +466,12 @@ impl<'a, N, I: SpIndex> TripletMatViewMutBase<'a, N, I> {
  #[cfg(test)]
  mod test {
  - use super::TripletMat;
  - use sparse::CsMatOwned;
  + use super::{TripletMat, TripletMatI};
  + use sparse::{CsMatOwned, CsMatOwnedI};
  #[test]
  fn triplet_incremental() {
  - let mut triplet_mat = TripletMat::with_capacity((4, 4), 6);
  + let mut triplet_mat = TripletMatI::with_capacity((4, 4), 6);
  // |1 2 |
  // |3 |
  // | 4|
  @@ -483,8 +483,8 @@ mod test {
  triplet_mat.add_triplet(3, 2, 5.);
  triplet_mat.add_triplet(3, 3, 6.);
  - let csc = triplet_mat.to_csc();
  - let expected = CsMatOwned::new_csc((4, 4),
  + let csc: CsMatOwnedI<_, i32> = triplet_mat.to_csc();
  + let expected = CsMatOwnedI::new_csc((4, 4),
  vec![0, 2, 3, 4, 6],
  vec![0, 1, 0, 3, 2, 3],
  vec![1., 3., 2., 5., 4., 6.]);
  