Add computability image hierarchy.
	
	* oln/core/abstract/image/computability: New.
	* oln/core/abstract/image/computability/hierarchy.hh: New.
	* oln/core/typedefs.hh (is_computed_type): New.
	* oln/core/image_entry.hh (is_computed_type): New in vtypes.
	* oln/core/abstract/image.hh (decl): Update.
	* oln/core/abstract/image/hierarchies.hh
	(image_hierarchy_wrt_computability): New.
	(hierarchy): Update ids.
	* oln/core/abstract/image/all.hh
	(include): Add computability/hierarchy.hh.
	* oln/core/1d/image1d.hh: Update.
	* oln/core/2d/image2d.hh: Likewise.
	* oln/core/3d/image3d.hh: Likewise.
	* oln/core/gen/mapimage.hh: Likewise.
	* oln/morpher/value_cast.hh: Likewise.
	* oln/morpher/thru_fun.hh: Likewise.
	* oln/morpher/internal/image_value_morpher.hh: Likewise.



git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@651 4aad255d-cdde-0310-9447-f3009e2ae8c0