Alien Ruin fix, various cherrypicked upstream fixes

Also adds new buildmode

code/modules/buildmode/effects/line.dm

@@ -0,0 +1,28 @@
+/obj/effect/buildmode_line
+	var/image/I
+	var/client/cl
+
+/obj/effect/buildmode_line/New(client/C, atom/atom_a, atom/atom_b, linename)
+	name = linename
+	loc = get_turf(atom_a)
+	I = image('icons/misc/mark.dmi', src, "line", 19.0)
+	var/x_offset = ((atom_b.x * 32) + atom_b.pixel_x) - ((atom_a.x * 32) + atom_a.pixel_x)
+	var/y_offset = ((atom_b.y * 32) + atom_b.pixel_y) - ((atom_a.y * 32) + atom_a.pixel_y)
+
+	var/matrix/mat = matrix()
+	mat.Translate(0, 16)
+	mat.Scale(1, sqrt((x_offset * x_offset) + (y_offset * y_offset)) / 32)
+	mat.Turn(90 - ATAN2(x_offset, y_offset)) // So... You pass coords in order x,y to this version of atan2. It should be called acsc2.
+	mat.Translate(atom_a.pixel_x, atom_a.pixel_y)
+
+	transform = mat
+	cl = C
+	cl.images += I
+
+/obj/effect/buildmode_line/Destroy()
+	if(I)
+		if(istype(cl))
+			cl.images -= I
+			cl = null
+		QDEL_NULL(I)
+	return ..()