Some region selection fixes

- CuboidSelection no longer deals with IncompleteRegionExceptions
- Fixed Polygonal2DSelection not passing its region to the selector
- Fixed Polygonal2DRegion not cloning the list it receives in its constructor
- Gave PolygonalRegionSelector a new constructor where it takes a list of points

src/main/java/com/sk89q/worldedit/regions/Polygonal2DRegion.java

@@ -76,7 +76,7 @@ public class Polygonal2DRegion implements Region {
      * @param maxY
      */
     public Polygonal2DRegion(LocalWorld world, List<BlockVector2D> points, int minY, int maxY) {
-        this.points = points;
+        this.points = new ArrayList<BlockVector2D>(points);
         this.minY = minY;
         this.maxY = maxY;
         hasY = true;

src/main/java/com/sk89q/worldedit/regions/Polygonal2DRegionSelector.java

@@ -80,6 +80,12 @@ public class Polygonal2DRegionSelector implements RegionSelector, CUIRegion {
         }
     }
 
+    public Polygonal2DRegionSelector(LocalWorld world, List<BlockVector2D> points, int minY, int maxY) {
+        final BlockVector2D pos2D = points.get(0);
+        pos1 = new BlockVector(pos2D.getX(), minY, pos2D.getZ());
+        region = new Polygonal2DRegion(world, points, minY, maxY);
+    }
+
     public boolean selectPrimary(Vector pos) {
         if (pos.equals(pos1)) {
             return false;