lualoader: Steamroll the box-drawing

- Add drawer.frame_styles to map out the kinds of characters we need for the
  different loader_menu_frame values
- Respect loader_menu_frame, default to double[*]
- (imp) Use loader.printc instead of print- print adds a newline to the
  output, which is not the right thing we want to be doing.
- (imp) Draw horizontal frames a little more efficiently- setting the cursor
  after every line segment is horribly inefficient, especially on serial
  consoles. Halve the number of characters written at the expense of an
  additional loop to draw the bottom frame, which is likely more efficient
  in the long run for some of less ideal scenarios.

[*] menu.4th(8) claims that the default here was single, but unset
loader_menu_frame yielded double and we didn't have any overrides in the
default loader.conf(5), so double it is.

stand/lua/drawer.lua

@@ -256,6 +256,36 @@ drawer.logodefs = {
 	},
 }
 
+drawer.frame_styles = {
+	-- Indexed by valid values for loader_menu_frame in loader.conf(5).
+	-- All of the keys appearing below must be set for any menu frame style
+	-- added to drawer.frame_styles.
+	["ascii"] = {
+		horizontal	= "-",
+		vertical	= "|",
+		top_left	= "+",
+		bottom_left	= "+",
+		top_right	= "+",
+		bottom_right	= "+",
+	},
+	["single"] = {
+		horizontal	= "\xC4",
+		vertical	= "\xB3",
+		top_left	= "\xDA",
+		bottom_left	= "\xC0",
+		top_right	= "\xBF",
+		bottom_right	= "\xD9",
+	},
+	["double"] = {
+		horizontal	= "\xCD",
+		vertical	= "\xBA",
+		top_left	= "\xC9",
+		bottom_left	= "\xC8",
+		top_right	= "\xBB",
+		bottom_right	= "\xBC",
+	},
+}
+
 function drawer.drawscreen(menu_opts)
 	-- drawlogo() must go first.
 	-- it determines the positions of other elements
@@ -306,42 +336,52 @@ function drawer.drawmenu(menudef)
 	return alias_table
 end
 
-
 function drawer.drawbox()
 	local x = drawer.box_pos_dim.x
 	local y = drawer.box_pos_dim.y
 	local w = drawer.box_pos_dim.w
 	local h = drawer.box_pos_dim.h
 
-	local hl = "\xCD"
-	local vl = "\xBA"
-
-	local tl = "\xC9"
-	local bl = "\xC8"
-	local tr = "\xBB"
-	local br = "\xBC"
-
-	screen.setcursor(x, y); print(tl)
-	screen.setcursor(x, y+h); print(bl)
-	screen.setcursor(x+w, y); print(tr)
-	screen.setcursor(x+w, y+h); print(br)
-
-	for i = 1, w-1 do
-		screen.setcursor(x+i, y)
-		print(hl)
-		screen.setcursor(x+i, y+h)
-		print(hl)
+	local framestyle = loader.getenv("loader_menu_frame") or "double"
+	local framespec = drawer.frame_styles[framestyle]
+	-- If we don't have a framespec for the current frame style, just don't
+	-- draw a box.
+	if framespec == nil then
+		return
 	end
 
-	for i = 1, h-1 do
-		screen.setcursor(x, y+i)
-		print(vl)
-		screen.setcursor(x+w, y+i)
-		print(vl)
+	local hl = framespec.horizontal
+	local vl = framespec.vertical
+
+	local tl = framespec.top_left
+	local bl = framespec.bottom_left
+	local tr = framespec.top_right
+	local br = framespec.bottom_right
+
+	screen.setcursor(x, y); loader.printc(tl)
+	screen.setcursor(x, y + h); loader.printc(bl)
+	screen.setcursor(x + w, y); loader.printc(tr)
+	screen.setcursor(x + w, y + h); loader.printc(br)
+
+	screen.setcursor(x + 1, y)
+	for _ = 1, w - 1 do
+		loader.printc(hl)
 	end
 
-	screen.setcursor(x+(w/2)-9, y)
-	print("Welcome to FreeBSD")
+	screen.setcursor(x + 1, y + h)
+	for _ = 1, w - 1 do
+		loader.printc(hl)
+	end
+
+	for i = 1, h - 1 do
+		screen.setcursor(x, y + i)
+		loader.printc(vl)
+		screen.setcursor(x + w, y + i)
+		loader.printc(vl)
+	end
+
+	screen.setcursor(x + (w / 2) - 9, y)
+	loader.printc("Welcome to FreeBSD")
 end
 
 function drawer.draw(x, y, logo)