slice of DenseVector

```
scala> import breeze.linalg.DenseVector
scala> val dvec = DenseVector((0 to 15).toArray)(0 to 15 by 3)
dvec: breeze.linalg.DenseVector[Int] = DenseVector(0, 3, 6, 9, 12, 15)

scala> dvec(1 to 5 by 2)
res0: breeze.linalg.DenseVector[Int] = DenseVector(1, 7, 13)
```
I expect that dvec(1 to 5 by 2) = DenseVector(3, 9, 15).
If I understand slice correctly, argument "start" should be multiplied by field "stride".