- convertPointField caused a seg-fault if the internal field was null
      - attempted to name the vtk object the name of the null field

+ minor clean-up

    - incompressible, Boussinesq variant of buoyantSimpleFoam
    - requires new fixedFluxBoussinesqBuoyantPressure bc on pd at walls
      to balance the flux generated by the temperature gradient

largest and smallest representable values.  Accessible directly and via pTraits.

- eliminated previous PackedBitRef class, the iterator does all of that and
  can also be used to (forward) traverse the list
- no const_iterator yet

- Note that PackedList is also a bit like DynamicList in terms of storage
  management and the append() method. Since the underlying storage in
  integer, any auto-vivified elements will also flood-fill the gaps with
  zero.

- removed Cmu from kOmegaSST models - not used
- general tidying up

- new members:  capacity(), two-argument resize()/setSize(), const storage()
- new static members: max_value(), packing(), etc.