pimpleFoam uses non-native collectives

In e.g. pimpleFoam it still uses the following non-native collectives:

• Pstream::scatter inside fileMonitor::updateStates (only if runTimeModifiable)
• Foam::gMax (from Foam::reduce) in CourantNo determination
• bound() from RASModels::kEpsilon
• reduce<bool, Foam::andOp > from p.needReference()

(done by adding a error::printStack(Pout) to UIPstream::read)

These could optionally be converted to native MPI calls.