Update tools.js's TOOL_RECTANGLE so that rectangles have sharp edges,…

… working around weirdness in latest Firefox

As discussed in #326,
the drawing of rectangles show a blurred/anti-aliased edge in the recent versions of Firefox.  This change restores sharp edges in Firefox.  The change is modeled after how the existing code  handles the degenerate case of drawing the rectangle (when the rectangle is either not as tall or not as wide as double the rectangle line width), but this version just draws four rectangles, one for each side.

src/tools.js

@@ -842,8 +842,13 @@
 					ctx.fillRect(x, y, w, h);
 					ctx.restore();
 				} else {
-					// @TODO: shouldn't that be ~~(stroke_size / 2)?
-					ctx.strokeRect(x + stroke_size / 2, y + stroke_size / 2, w - stroke_size, h - stroke_size);
+ 					ctx.save();
+ 					ctx.fillStyle = ctx.strokeStyle;
+ 					ctx.fillRect(x, y, stroke_size, h);
+ 					ctx.fillRect(x+w-stroke_size, y, stroke_size, h);
+ 					ctx.fillRect(x, y, w, stroke_size);
+ 					ctx.fillRect(x, y+h-stroke_size, w, stroke_size);
+ 					ctx.restore();
 				}
 			}
 		},