added OMP pragmas to PFFT potential ( didn't see a permermance increase )
added OMP pragmas to PFFT potential ( didn't see a permermance increase )

cholla-hydro/cholla,evaneschneider/cholla,cholla-hydro/cholla,evaneschneider/cholla,cholla-hydro/cholla,evaneschneider/cholla,cholla-hydro/cholla,evaneschneider/cholla