Use Wfact when it is available

[YingboMa]

This PR depends on SciML/DiffEqBase.jl#303

[YingboMa]

using OrdinaryDiffEq, ModelingToolkit, Test
function lotka(du,u,p,t)
  x = u[1]
  y = u[2]
  du[1] = p[1]*x - p[2]*x*y
  du[2] = -p[3]*y + p[4]*x*y
end

prob = ODEProblem(lotka,[1.0,1.0],(0.0,1.0),[1.5,1.0,3.0,1.0])
de = ModelingToolkit.modelingtoolkitize(prob)
prob2 = remake(prob, f=ODEFunction(de..., Val(false), Wfact=true))

sol = solve(prob, KenCarp4())

@test Array( solve(prob2, Rodas5()) ) ≈ Array( solve(prob, Rodas5()) )
@test Array( solve(prob2, KenCarp4(), tstops=sol.t, adaptive=false) ) ≈ Array( solve(prob, KenCarp4(), tstops=sol.t, adaptive=false) )

julia> @test Array( solve(prob2, Rodas5()) ) ≈ Array( solve(prob, Rodas5()) )
Test Passed

julia> @test Array( solve(prob2, KenCarp4(), tstops=sol.t, adaptive=false) ) ≈ Array( solve(prob, KenCarp4(), tstops=sol.t, adaptive=false) )
Test Passed

[codecov]

Codecov Report

Merging #847 into master will decrease coverage by 1.19%.
The diff coverage is 20%.

@@            Coverage Diff            @@
##           master     #847     +/-   ##
=========================================
- Coverage   80.35%   79.15%   -1.2%     
=========================================
  Files          90       90             
  Lines       29846    29849      +3     
=========================================
- Hits        23982    23628    -354     
- Misses       5864     6221    +357

Impacted Files	Coverage Δ
src/derivative_utils.jl	55.03% <20%> (-20.94%)	⬇️
src/perform_step/composite_perform_step.jl	30.43% <0%> (-47.83%)	⬇️
src/composite_algs.jl	60% <0%> (-36%)	⬇️
src/composite_solution.jl	23.8% <0%> (-33.34%)	⬇️
src/derivative_wrappers.jl	56.6% <0%> (-13.21%)	⬇️
src/caches/basic_caches.jl	74.07% <0%> (-8.69%)	⬇️
src/cache_utils.jl	8.33% <0%> (-8.34%)	⬇️
src/perform_step/fixed_timestep_perform_step.jl	89.74% <0%> (-7.98%)	⬇️
src/perform_step/rosenbrock_perform_step.jl	90.68% <0%> (-7.97%)	⬇️
... and 20 more

---

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[coveralls]

Coverage increased (+9.9%) to 88.124% when pulling 05dc945 on myb/Wfact into 2749f37 on master.

[ChrisRackauckas]

Waiting on JuliaNLSolvers/NLsolve.jl#220 I think.