[BE] Fix handling of mixed determined systems

[kabdelhak]

• add all variable indices to artifical functions in adjacency matrix
• ticket #5170

[kabdelhak]

This actually fixes ticket #5170, but several other models like ../simulation/modelica/resolveLoops/ElectricalCircuit1.mos fail with different results.

Feel free to comment the code!

[casella]

I can't see the results of the testsuite. Maybe you can run it on this PR, so we can check?

[OpenModelica-Hudson]

The test suite is unstable according to OpenModelica_TEST_PULL_REQUEST 2019-05-10_16-24-49.