No sanity check when we use 2 _

[SergeStinckwich]

When we define a model like:

KModel SEIRS
    attribute: #(status -> S E I R);
    parameters: #(beta lambda gamma mu sigma nu);
    lambda: #(beta*I/N);
    equations: #(
         S:t=mu*N - lamda*S - mu*S + nu*R.
         E:t=lambda*S - sigma*E - mu*E.
         I:t=sigma*E - gamma*I - mu*I.
         R:t=gamma*I - mu*R - nu*R.).

KModel MultiSpecies
    attribute: #(species -> humans birds).

Composition Influenza
    model: 'SEIRS';
    model: 'MultiSpecies'.

Scenario Scr1
    on: 'Influenza';
    mu_species_species: #(0.000365 0.00137);

no sanity check is done on mu_species_species.