Can get Gridded() object at vector, why not scaled one?

I can get values at a vector of points from a gridded interp object, but not from a scaled version of that same object. intended, not, or my mistake?

this is related to #128 .

```
julia> xy = [3z+2y for z in linspace(0.0,1,10),y in 0:0.2:1]
julia> itp = interpolate((1:10,1:6),xy,(Gridded(Linear()),NoInterp()
))
10×6 Interpolations.GriddedInterpolation{Float64,2,Float64,Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Tuple{Array{Int64,1},Array{Int64,1}},0}:
0.0 0.4 0.8 1.2 1.6 2.0
0.333333 0.733333 1.13333 1.53333 1.93333 2.33333
0.666667 1.06667 1.46667 1.86667 2.26667 2.66667
1.0 1.4 1.8 2.2 2.6 3.0
1.33333 1.73333 2.13333 2.53333 2.93333 3.33333
1.66667 2.06667 2.46667 2.86667 3.26667 3.66667
2.0 2.4 2.8 3.2 3.6 4.0
2.33333 2.73333 3.13333 3.53333 3.93333 4.33333
2.66667 3.06667 3.46667 3.86667 4.26667 4.66667
3.0 3.4 3.8 4.2 4.6 5.0

julia> itp[3.3,1:6]
1×6 Array{Float64,2}:
0.766667 1.16667 1.56667 1.96667 2.36667 2.76667

julia> sitp =scale( itp ,linspace(0.0,1.0,10),1:6)
10×6 Interpolations.ScaledInterpolation{Float64,2,Interpolations.GriddedInterpolation{Float64,2,Float64,Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Tuple{Array{Int64,1},Array{Int64,1}},0},Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Interpolations.OnGrid,Tuple{LinSpace{Float64},UnitRange{Int64}}}:
3.0 3.4 3.8 4.2 4.6 5.0
6.0 6.4 6.8 7.2 7.6 8.0
9.0 9.4 9.8 10.2 10.6 11.0
12.0 12.4 12.8 13.2 13.6 14.0
15.0 15.4 15.8 16.2 16.6 17.0
18.0 18.4 18.8 19.2 19.6 20.0
21.0 21.4 21.8 22.2 22.6 23.0
24.0 24.4 24.8 25.2 25.6 26.0
27.0 27.4 27.8 28.2 28.6 29.0
30.0 30.4 30.8 31.2 31.6 32.0

julia> sitp[0.3,1:6]
ERROR: BoundsError: attempt to access 10×6 Interpolations.ScaledInterpolation{Float64,2,Interpolations.GriddedInterpolation{Float64,2,Float64,Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Tuple{Array{Int64,1},Array{Int64,1}},0},Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Interpolations.OnGrid,Tuple{LinSpace{Float64},UnitRange{Int64}}} at index [0.3,1:6]
in throw_boundserror(::Interpolations.ScaledInterpolation{Float64,2,Interpolations.GriddedInterpolation{Float64,2,Float64,Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Tuple{Array{Int64,1},Array{Int64,1}},0},Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Interpolations.OnGrid,Tuple{LinSpace{Float64},UnitRange{Int64}}}, ::Tuple{Float64,UnitRange{Int64}}) at ./abstractarray.jl:355
in checkbounds at ./abstractarray.jl:284 [inlined]
in _getindex at ./multidimensional.jl:270 [inlined]
in getindex(::Interpolations.ScaledInterpolation{Float64,2,Interpolations.GriddedInterpolation{Float64,2,Float64,Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Tuple{Array{Int64,1},Array{Int64,1}},0},Tuple{Interpolations.Gridded{Interpolations.Linear},Interpolations.NoInterp},Interpolations.OnGrid,Tuple{LinSpace{Float64},UnitRange{Int64}}}, ::Float64, ::UnitRange{Int64}) at ./abstractarray.jl:752
```