WIP: Refactoring JuMP.solve

[yeesian]

Because it looks too forbidding, and I hope it might eventually be more like

solve(m::JuMP.AbstractModel, args...; kwargs...) =
    error("`solve()` not implemented for $(typeof(m))")

function solve(
        m::JuMP.Model;
        suppress_warnings=false,
        relaxation=false
    )
    traits = ProblemTraits(m, relaxation=relaxation) # to determine what solvers we can use
    build!(m, traits=traits, suppress_warnings=suppress_warnings, relaxation=relaxation)
    MathProgBase.optimize!(m.internalModel)
    stat = MathProgBase.status(m.internalModel)
    update!(m, stat, traits, relaxation)
    stat
end

The idea is to let ProblemTraits capture all information that needs to be known about the Model and Problem, for build! and update! to perform the necessary pre-solve and post-solve work.

[mlubin]

Travis is failing because there's a very delicate interplay of return status, solver pathway, and whether we ask the solver for primal and dual solutions. Everything will change with JuliaOpt/MathProgBase.jl#156 which I'm planning on working on soon, so you may want to hold off on this PR.

[yeesian]

no hurry at all

[mlubin]

Closing, we can revisit if needed after JuliaOpt/MathProgBase.jl#164