fix failure of non-regression test SMESH_TEST/Grids/smesh/mesh_Projection_2D/A0

  Allow assigning "3D Extrusion" algo to a computed 2D mesh w/o
  clearing existing 2D elements

-  void cleanDependsOn( bool keepSupportedsubMeshes = false );
+  void cleanDependsOn( SMESH_Algo* algoRequiringCleaning=0 );