Tile Assignment Check

[ryanmrichard]

Consider the following code which intends to put the diagonal of a rank 4 tensor into a rank 2 tensor:

auto t4 = makes_a_rank_4_tensor();
auto t2 = makes_uninitialized_rank_2_tensor();
for(auto itr = t2.begin(); itr != t2.end(); ++itr){
    auto ij = itr.index();
    // Bug because user unintentionally copies the range and not just the data
    t2.set(ij, t4.find({ij[0], ij[1], ij[0], ij[1]}));
}

This actually compiles and "works" (the resulting tensor can be printed, but results in errors in most other circumstances since the tensor is rank 2, but has rank 4 tiles). I think set should raise an error in this scenario. Not a pressing issue, but wanted to make a note of it before I forgot.