Fails on master because of "world" error

```julia
julia> Pkg.test("NLopt")
```

```
INFO: Testing NLopt
in callback catch
ERROR: LoadError: LoadError: MethodError: no method matching myfunc(::Array{Float64,1}, ::Array{Float64,1})
The applicable method may be too new: running in world age 20977, while current world is 20981.
```