Do not sort variable names

[dpsanders]

julia> vars
(x1(), x2(), x3(), x4(), x5(), x6(), x7(), x8(), x9(), x10())

julia> C.forward.code
quote
    #= /Users/davidsanders/.julia/packages/IntervalConstraintProgramming/ul86T/src/code_generation.jl:192 =#
    t->begin
            #= /Users/davidsanders/.julia/packages/IntervalConstraintProgramming/ul86T/src/code_generation.jl:192 =#
            #= /Users/davidsanders/.julia/packages/IntervalConstraintProgramming/ul86T/src/code_generation.jl:193 =#
            (x1, x10, x2, x3, x4, x5, x6, x7, x8, x9) = t

The variables should not be sorted here.

cc @Yashcodes