Propagated the changes everywhere

src/cell.c

src/cell.h

src/debug.c

src/engine.c

src/engine.h

src/gravity/Default/gravity_part.h

src/hydro/Gadget2/hydro.h

src/hydro/Gadget2/hydro_debug.h

src/hydro/Gadget2/hydro_part.h

src/runner.c

src/runner_doiact.h

src/runner_doiact_grav.h

src/space.c