Many failed regression tests

Today there were many failed regression tests: http://amas.web.psi.ch/opal/regressionTests/master/results_2019-05-10.xml

There were four merge requests (issue assigned to the authors of these):

1. !82 (merged)
2. !87 (merged)
3. !90 (merged)
4. !92 (merged)

I had a quick look and I suspect this change in the PoissonSolver https://gitlab.psi.ch/OPAL/src/blob/master/src/Solvers/FFTPoissonSolver.cpp:

@@ -388,7 +388,7 @@ void FFTPoissonSolver::computePotentialDKS(Field_t &rho) {
    if (Ippl::myNode() == 0) {
        IpplTimings::startTimer(GreensFunctionTimer_m);
-       integratedGreensFunction();
+       integratedGreensFunctionDKS();
        IpplTimings::stopTimer(GreensFunctionTimer_m);
        //transform the greens function
        int dimsize[3] = {2*nr_m[0], 2*nr_m[1], 2*nr_m[2]};