message: another try to fix it on osx
diff: * the Free Software Foundation, either version 3 of the License, or
  * (at your option) any later version.
  *
  + *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  @@ -48,6 +49,11 @@ namespace Gudhi
  namespace Gudhi_stat
  {
  +//predeclaration
  +class Persistence_landscape_on_grid;
  +template < typename operation >
  +Persistence_landscape_on_grid operation_on_pair_of_landscapes_on_grid( const Persistence_landscape_on_grid& land1 , const Persistence_landscape_on_grid& land2 );
  +
  /**
  * A clas implementing persistence landascpes by approximating them on a collection of grid points. * Persistence landscapes on grid allow vertorization, computations of distances, computations
  * of projections to Real, computations of averages and scalar products. Therefore they implement suitable interfaces.
  @@ -282,6 +288,9 @@ public:
  return out;
  }
  + template < typename oper >
  + friend Persistence_landscape_on_grid operation_on_pair_of_landscapes_on_grid( const Persistence_landscape_on_grid& land1 , const Persistence_landscape_on_grid& land2 );
  +
  /**
  * A function that computes the value of a landscape at a given point. The parameters of the function are: unsigned level and double x.
  @@ -344,8 +353,6 @@ public:
  return line.first*x+line.second;
  }
  - protected:
  - template < typename oper > friend Persistence_landscape_on_grid operation_on_pair_of_landscapes_on_grid( const Persistence_landscape_on_grid& land1 , const Persistence_landscape_on_grid& land2 );
  public:
  /**
  