Add support for multi-line text entries

Xwt.Gtk/Xwt.GtkBackend/TextEntryBackend.cs

@@ -152,6 +152,10 @@ namespace Xwt.GtkBackend
 				Widget.HasFrame = value;
 			}
 		}
+
+		public bool MultiLine {
+			get; set;
+		}
 		
 		public override void EnableEvent (object eventId)
 		{

Xwt.Mac/Xwt.Mac/TextEntryBackend.cs

@@ -49,6 +49,7 @@ namespace Xwt.Mac
 			} else {
 				ViewObject = new CustomTextField (EventSink, ApplicationContext);
 			}
+			MultiLine = false;
 		}
 		
 		protected override Size GetNaturalSize ()
@@ -103,6 +104,23 @@ namespace Xwt.Mac
 			}
 		}
 
+		public bool MultiLine {
+			get {
+				return Widget.Cell.UsesSingleLineMode;
+			}
+			set {
+				if (value) {
+					Widget.Cell.UsesSingleLineMode = true;
+					Widget.Cell.Scrollable = true;
+					Widget.Cell.Wraps = false;
+				} else {
+					Widget.Cell.UsesSingleLineMode = false;
+					Widget.Cell.Scrollable = false;
+					Widget.Cell.Wraps = true;
+				}
+			}
+		}
+
 		public override void SetFocus ()
 		{
 			Widget.BecomeFirstResponder ();

Xwt.WPF/Xwt.WPFBackend/TextEntryBackend.cs

@@ -78,6 +78,11 @@ namespace Xwt.WPFBackend
 			set { TextBox.ShowFrame = value; }
 		}
 
+		// TODO
+		public bool MultiLine {
+			get; set;
+		}
+
 		public override void EnableEvent (object eventId)
 		{
 			base.EnableEvent (eventId);

Xwt/Xwt.Backends/ITextEntryBackend.cs

@@ -34,6 +34,7 @@ namespace Xwt.Backends
 		string PlaceholderText { get; set; }
 		bool ReadOnly { get; set; }
 		bool ShowFrame { get; set; }
+		bool MultiLine { get; set; }
 	}
 	
 	public interface ITextEntryEventSink: IWidgetEventSink

Xwt/Xwt/TextEntry.cs

@@ -94,6 +94,12 @@ namespace Xwt
 			set { Backend.ShowFrame = value; }
 		}
 		
+		[DefaultValue (true)]
+		public bool MultiLine {
+			get { return Backend.MultiLine; }
+			set { Backend.MultiLine = value; }
+		}
+
 		protected virtual void OnChanged (EventArgs e)
 		{
 			if (changed != null)