* oln/core/neighborhood1d.hh: Fix add method, neighborhood1d is
	not centered

	// Neighborhoods
  	// =============
  	// These objects are like Windows, except they have
  	// some additional properties (a point is not in its neighborhood,
  	// the neighbor of a point should have the point in its neighborhood).
  	// For this reason, they have types distinct from the windows:
  	// neighborhood1d, neighborhood2d, neighborhood3d.
  	// The interface is just the same as the windows.

	So a neighborhood was a symetric windows widthout the center.

	Fix neighb_c2() and mk_neighb_segment() : now, the symetric
	dpoint is automatically added by add method.

	* oln/core/neighborhood2d.hh: Likewise for add(), neighb_c4(),
	neighb_c8() and mk_neighb_rectangle() methods.

	* oln/core/neighborhood3d.hh: Likewise for add(),  neighb_c6(),
	neighb_c18(), neighb_c26() and mk_neighb_block() methods.

    prcs2git-id: 0_5.72