- keeps sources in sync for the 1.6 release and it'll get fiddled with
  for the 1.7 release anyhow

- IMO we should retain ReleaseNotes-1.5 and distribute it with OpenFOAM-1.6
  as well.

- rename thermalDissipationEff() -> thermalDissipationEquilibrium()

- first stab at a simple runtime selection for extra turbulence-related
  features

- the code duplication seems to indicate that a common ancestor
  for compressible and incompressible turbulence models could be good

- thermalDissipation()
  corresponds to the energy lost due to viscous efffects and
  what exits the energy cascade via dissipation.

- thermalDissipationEff()
  corresponds to the energy lost due to effective viscous efffects.
  Everything that is lost from momentum. Thus essentially assumes
  turbulent equilibrium, but is what STAR-CD and Fluent seem to be using.
  Thus even if it's wrong, provide it anyhow.

- minor consistency update in comments