FLASH4 complete API

   This function returns an indication whether the most
   recent call to Hydro has, as a side effect, completely
   updated the gravitational potential in the UNK variable
   GPOT (and other state related to gravitational forces
   if applicable - see implementation of sink paticles).

   Code that is responsible for updating GPOT to the most
   recent solution of the Poisson equation for gravity
   (typically by calling Gravity_potentialListOfBlocks
   at the end of each time advance iteration in
   Driver_evolveFlash) MAY use this function to avoid
   an unnecessary additional call to the Poisson solver.

   An implementation of this interface should only return
   TRUE when it is certain that an additional call to
   Gravity_potentialListOfBlocks would not change
   results.

   For any constant-in-time Gravity implementations,
   the return value does not matter.