Join of identical non-unique indexes is not correct

[pityka]

  "Outer join of same non-unique indexes " in {
      val ix1 = Index(0, 0)
      val ix2 = Index(0, 0)
      val res = ix1.join(ix2, how = index.OuterJoin)
      /*
        Outer join two columns with repeated values should generate all possible pairs

        Correct assertions:
      res.index must_== Index(0, 0, 0, 0)
      res.lTake.get must_== Array(0, 0, 1, 1)
      res.rTake.get must_== Array(0, 1, 0, 1)

      However the current implementation has a shortcut for identical indexes and passes these:
       */
      res.index must_== Index(0, 0)
      res.lTake must_== None
      res.rTake must_== None

    }

This is because in the implementation there is a shortcut:

def join(left: Index[T], right: Index[T], how: JoinType): ReIndexer[T] = {
    if (left == right) {
      ReIndexer(None, None, right)
    } else if..

The above condition should check for uniqueness.