Frep evaluations shouldn't allocate.

[sjkelly]

jb/tupleoverhaul doesn't seem to get rid of the allocations during FRep eval. There are some deeper design issues here:

julia> u = union(Sphere(2, (2,3,4)), Sphere(4, (4,5,6)), Sphere(5, (7,8,9)))
Descartes.CSGUnion{3,Int64}(Descartes.Sphere{3,Int64}(2,(2,3,4)),Descartes.CSGUnion{3,Int64}(Descartes.Sphere{3,Int64}(4,(4,5,6)),Descartes.Sphere{3,Int64}(5,(7,8,9))))

julia> a = FRep(u)
Descartes.FRep{3,Int64}(Descartes.CSGUnion{3,Int64}(Descartes.Sphere{3,Int64}(2,(2,3,4)),Descartes.CSGUnion{3,Int64}(Descartes.Sphere{3,Int64}(4,(4,5,6)),Descartes.Sphere{3,Int64}(5,(7,8,9)))),csgunion_frep)

julia> @code_lowered a.func(1,2,3)
1-element Array{Any,1}:
 :($(Expr(:lambda, Any[:x,:y,:z], Any[Any[],Any[Any[:x,Any,0],Any[:y,Any,0],Any[:z,Any,0]],Any[Any[:u,Descartes.CSGUnion{3,Int64},1]],0], :(begin  # /home/steve/.julia/v0.4/Descartes/src/frep.jl, line 15:
        return min((FRep((top(getfield))(u,:left)::Any)::Any)(x,y,z)::Any,(FRep((top(getfield))(u,:right)::Any)::Any)(x,y,z)::Any)::Any
    end::Any))))

[sjkelly]

More atomic case:

 julia> b = FRep(Sphere(4, (1,2,3)))
Descartes.FRep{3,Int64}(Descartes.Sphere{3,Int64}(4,(1,2,3)),sphere_frep)

julia> @code_lowered b.func(1,2,3)
1-element Array{Any,1}:
 :($(Expr(:lambda, Any[:x,:y,:z], Any[Any[],Any[Any[:x,Any,0],Any[:y,Any,0],Any[:z,Any,0]],Any[Any[:s,Descartes.Sphere{3,Int64},1]],0], :(begin  # /home/steve/.julia/v0.4/Descartes/src/frep.jl, line 7:
        return sqrt((x - getindex((top(getfield))(s,:location)::Any,1)::Any)::Any ^ 2::Any + (y - getindex((top(getfield))(s,:location)::Any,2)::Any)::Any ^ 2::Any + (z - getindex((top(getfield))(s,:location)::Any,3)::Any)::Any ^ 2::Any::Any)::Any - (top(getfield))(s,:radius)::Any::Any
    end::Any))))

So it looks like closures blow at type inference.