This provides more flexibility in specifying the allowed internal and boundary
extrema.
For driftFluxFoam and other settling problems it is beneficial to set the
boundaryExtremaCoeff to 1 to allow rapid accumulation of the partials on the
bottom wall (which was the previous default behaviour) but this is not suitable
for many Euler-Euler cases for which a uniform etrema coefficient is preferable,
either 0 or a small value.
Now by default boundaryExtremaCoeff is set to extremaCoeff which defaults to 0
which provides the behaviour before
OpenFOAM-dev commit cb2bc60fa5
and the driftFluxFoam tutorials have been updated adding
boundaryExtremaCoeff 1;
to the MULES controls in fvSolution so reproduce the previous behaviour.
441b7e041b