/ log construction.

Construction		Source		Result
			0	empty window
	0	shallow pit	#	half-built log wall
	#	half-built log wall	LINE_OXOX	log wall
	&	broken log wall	LINE_OXOX	chipped log wall
	0	pit	#	palisade wall
			.	primitive floor
	0	pit	+	palisade gate
	#	half-built log wall	o	log wall with embrasure
	0	pit	o	palisade wall with embrasure
		is:DIGGABLE
	.	rock floor
	#	solid rock
	~	flowing shallow water	8	dock
	|	deep dock pile	#	deep dock frame
	~	shallow water	8	shallow bridge
	#	fence post	LINE_OXOX	rammed earth wall
			#	log stool
			+	decorative tree