Should broadcast work on distributed arrays?

I rather like the second behavior and hoping it could be made to work
by overloading the dot in broadcast.

```
a = distribute(1:5)
(x->x+1).(a)
5-element Array{Int64,1}:
 2
 3
 4
 5
 6
```

```
map(x->x+1,a)
5-element DistributedArrays.DArray{Int64,1,Array{Int64,1}}:
 2
 3
 4
 5
 6
```