Handling of times around daylight savings change

I suppose this will only reproduce when your computer is set to a timezone where the daylight savings time change happens on 30 March, but it should be easy to adapt:

```
(R.zoo([| 1.0 |], [| System.DateTime(2014,3,30).AddHours(0.0) |]) |> R.index).Print()
// "2014-03-30 UTC"

(R.zoo([| 1.0 |], [| System.DateTime(2014,3,30).AddHours(1.0) |]) |> R.index).Print()
// "2014-03-30 01:00:00 UTC"

(R.zoo([| 1.0 |], [| System.DateTime(2014,3,30).AddHours(2.0) |]) |> R.index).Print()
// "2014-03-30 01:00:00 UTC"

(R.zoo([| 1.0 |], [| System.DateTime(2014,3,30).AddHours(3.0) |]) |> R.index).Print()
// "2014-03-30 02:00:00 UTC"
```

The odd thing is that the second and third values print as the same time when they come back from R (possibly because at 1am, the UK clock jumps forward to 2am).

I have not investigated this further yet - so I'm not sure whether this is an issue with passing data into R or with getting data from R.