create InputInterpolation regrid regrid_impl ~InputInterpolation

regrid_impl() virtual double pism::InputInterpolation::regrid_impl ( const SpatialVariableMetadata &  metadata, const pism::File &  file, int  record_index, const Grid &  grid, petsc::Vec &  output  ) const protectedpure virtual Implemented in pism::InputInterpolation3D, and pism::InputInterpolationYAC. Referenced by regrid().