Bug with multiple variables

[dpsanders]

The following is supposed to create two "independent" affine variables:

julia> x = Affine(-1..1, 1, 2)   # "number 1 of 2"
affine=⟨0.0; [0.0]; [0, 0]⟩; range=[-1, 1]

julia> y = Affine(-1..1, 2, 2)  # "number 2 of 2"
affine=⟨0.0; [0.0, 1.0]; [0, 0]⟩; range=[-1, 1]

julia> x - y
ERROR: MethodError: no method matching -(::AffineArithmetic.Aff{1,Float64}, ::AffineArithmetic.Aff{2,Float64})