- still not consistent for pd as does not include buoyancy effects

while(runTime.loop())
{
...
}

idiom.

Demonstrated in the shallowWaterFoam solver.

- track previous time index and to avoid recalculating averages.
- make sure averages are up-to-date before calling write

- added end() method to functionObject, functionObjectList & associated classes
- moved outputFilters from src/sampling -> src/OpenFOAM/db/functionObjects

- this (now deprecated) idiom:
      for (runTime++; !runTime.end(); runTime++) { ... }
  has a few problems:
    * stop-on-next-write will be off-by-one (ie, doesn't work)
    * function objects are not executed on exit with runTime.end()
  Fixing these problems is not really possible.

- this idiom
      while (runTime.run())
      {
          runTime++;
          ...
      }
  works without the above problems.