Test mixintprog-based resolve(). The function is just Pkg.update() up to the call to Metadata.resolve(), with the resolve() code inlined.

myresolvetst.jl

require("pkg")

myresolve() = Pkg.cd_pkgdir() do
    have = (String=>ASCIIString)[]
    reqs = Metadata.parse_requires("REQUIRE")
    Git.each_submodule(false) do pkg, path, sha1
        if pkg != "METADATA"
            have[pkg] = sha1
        end
    end
    sort!(reqs)

    pkgs = Metadata.packages()
    vers = Metadata.versions(pkgs)
    deps = Metadata.dependencies(pkgs,vers)

    n = length(vers)
    z = zeros(Int,n)
    u = ones(Int,n)

    G  = [ v == d[1]        ? 1 : 0  for v=vers, d=deps ]
    G *= [ contains(d[2],v) ? 1 : 0  for d=deps, v=vers ]
    G += [ Metadata.older(a,b)       ? 2 : 0  for a=vers, b=vers ]
    I = find(G)
    W = zeros(Int,length(I),n)
    for (r,i) in enumerate(I)
        W[r,rem(i-1,n)+1] = -1
        W[r,div(i-1,n)+1] = G[i]
    end
    mipopts = GLPK.IntoptParam()
    mipopts["msg_lev"] = GLPK.MSG_ERR
    mipopts["presolve"] = GLPK.ON
    _, ws, flag, _ = LinProgGLPK.mixintprog(u,W,-ones(Int,length(I)),nothing,nothing,u,nothing,nothing,mipopts)
    if flag != 0
        msg = sprint(print_linprog_flag, flag)
        error("resolve() failed: $msg.")
    end
    w = iround(ws)

    V = [ p == v.package ? 1 : 0                     for p=pkgs, v=vers ]
    R = [ contains(r,v) ? -1 : 0                     for r=reqs, v=vers ]
    D = [ d[1] == v ? 1 : contains(d[2],v) ? -1 : 0  for d=deps, v=vers ]
    b = [  ones(Int,length(pkgs))
          -ones(Int,length(reqs))
          zeros(Int,length(deps)) ]

    _, xs, flag, flag2 = LinProgGLPK.mixintprog(w,[V;R;D],b,nothing,nothing,z,u,nothing,mipopts)
    if flag != 0
        msg = sprint(print_linprog_flag, flag)
        error("resolve() failed: $msg.")
    end
    x = bool(xs)
    h = (String=>ASCIIString)[]
    for v in vers[x]
        h[v.package] = readchomp("METADATA/$(v.package)/versions/$(v.version)/sha1")
    end
    return h
end