Reworked the internal CMap, it now does not know what a terrain or an actor is, instead the map objects are just textures, positioned on a z-order, 
each map object can tell if it can be seen, remembered, ...
Trees are now made of two or more map objects, a patch of grass and one or more tree, randomly placed on the tile, to make forests look less tilish


git-svn-id: http://svn.net-core.org/repos/t-engine4@863 51575b47-30f0-44d4-a5cc-537603b46e54