Creating a view (SubArray) of a Vector allocates memory

On 0.5 as well as the latest nightly, for matrices,
```julia
@benchmark view(a, 1:2, 1:2) setup = (a = rand(3, 3))
```
results in zero allocation.

However,
```julia
@benchmark view(a, 1:2) setup = (a = rand(3))
```
results in 48 bytes of allocation and is almost 6 times slower. I haven't been able to figure out what in `subarray.jl` causes this.
