Fixed Borders on XXX Pos.Center bugs

UICatalog/Scenarios/BordersOnFrameView.cs

@@ -45,7 +45,7 @@ namespace UICatalog.Scenarios {
 			button.Clicked += () => MessageBox.Query (20, 7, "Hi", "I'm a FrameView?", "Yes", "No");
 			var label = new Label ("I'm a FrameView") {
 				X = Pos.Center (),
-				Y = Pos.Center () - 3,
+				Y = Pos.Top (button) - 1,
 			};
 			var tf2 = new TextField ("1234567890") {
 				X = Pos.AnchorEnd (10),

UICatalog/Scenarios/BordersOnToplevel.cs

@@ -45,7 +45,7 @@ namespace UICatalog.Scenarios {
 			button.Clicked += () => MessageBox.Query (20, 7, "Hi", "I'm a Toplevel?", "Yes", "No");
 			var label = new Label ("I'm a Toplevel") {
 				X = Pos.Center (),
-				Y = Pos.Center () - 3,
+				Y = Pos.Top (button) - 1,
 			};
 			var tf2 = new TextField ("1234567890") {
 				X = Pos.AnchorEnd (10),

UICatalog/Scenarios/BordersOnWindow.cs

@@ -44,7 +44,7 @@ namespace UICatalog.Scenarios {
 			button.Clicked += () => MessageBox.Query (20, 7, "Hi", "I'm a Window?", "Yes", "No");
 			var label = new Label ("I'm a Window") {
 				X = Pos.Center (),
-				Y = Pos.Center () - 3,
+				Y = Pos.Top (button) - 1,
 			};
 			var tf2 = new TextField ("1234567890") {
 				X = Pos.AnchorEnd (10),