Fix issues in distBag.addBulk

[Guillaume-Helbecque]

In the addBulk procedure of the distBag data structure, things are as follows:

inline proc ref addElements(elts): int
    {
      var size = elts.size;
      ...
      // add the elements to the tail
      for elt in elts[0..#size] do block.pushTail(elt);
      tail += size;
      ...
    }

This produces an issue when the input elts is not 0-based (e.g., array slices). For example,

const A: [0..9] int = [0,1,2,3,4,5,6,7,8,9];
var bag = new distBag(int);
bag.addBulk(A[2..9], 0);
writeln(bag);

returns [2, 3, 4, 5, 6, 7, 0, 0] instead of [2, 3, 4, 5, 6, 7, 8, 9].

A fix for this is to iterate over elts without specifying the domain, and use a counter to make sure that we do not insert more elements than we can. I also update the tests to make sure that this bug doesn't come back in the future.

[Guillaume-Helbecque]

While working on a test failure, I noticed that there was another tiny issue in the way we compute the number of elements to insert when the maximum capacity of a segment is reached. For some reasons, this was hidden in the previous tests. I thus provided more tests to capture this.

[lydia-duncan]

I'm never gonna say no to more tests XD I'll try to take another look today, got a meeting coming up in five minutes

[lydia-duncan]

Looks good now, thanks! I'll merge this on Monday