For most multiphase flows it is more appropriate to evaluate the total pressure
from the static pressure obtained from p_rgh rather than from p_rgh directly.
The FOAM file format has not changed from version 2.0 in many years and so there
is no longer a need for the 'version' entry in the FoamFile header to be
required and to reduce unnecessary clutter it is now optional, defaulting to the
current file format 2.0.
