(svn r6406) -Codechange: Rename TileOffsByDir to TileOffsByDiagDir because it accepts

DiagDirections, and add TileOffsByDir that handles Directions.
-Codechange: Make the treeloop use TileOffsByDir().

clear_cmd.c

@@ -729,7 +729,7 @@ void GenerateClearTile(void)
 				SetClearGroundDensity(tile, CLEAR_ROCKS, 3);
 				do {
 					if (--j == 0) goto get_out;
-					tile_new = tile + TileOffsByDir(GB(Random(), 0, 2));
+					tile_new = tile + TileOffsByDiagDir(GB(Random(), 0, 2));
 				} while (!IsTileType(tile_new, MP_CLEAR) || IsClearGround(tile_new, CLEAR_DESERT));
 				tile = tile_new;
 			}