fix #436 - Debugger always steps into external code

I've restored the "Use 'Just My Code' feature for stepping" option

src/AddIns/Debugger/Debugger.AddIn/Options/DebuggingOptionsPanel.xaml

@@ -36,6 +36,8 @@
 		</GroupBox>
 		<GroupBox Margin="5" Header="{sd:Localize Dialog.Options.IDEOptions.Debugging.WithoutSource}">
 			<widgets:StackPanelWithSpacing SpaceBetweenItems="5">
+				<CheckBox Content="{sd:Localize Dialog.Options.IDEOptions.Debugging.Stepping.EnableJustMyCode}"
+				          IsChecked="{sd:OptionBinding debugger:DebuggingOptions.EnableJustMyCode}" />
 				<CheckBox Content="{sd:Localize Dialog.Options.IDEOptions.Debugging.AskForArguments}"
 				          IsChecked="{sd:OptionBinding debugger:DebuggingOptions.AskForArguments}" />
 				<CheckBox Content="{sd:Localize Dialog.Options.IDEOptions.Debugging.BreakAtBeginning}"

src/AddIns/DisplayBindings/ILSpyAddIn/ILSpySymbolSource.cs

@@ -16,7 +16,7 @@ namespace ICSharpCode.ILSpyAddIn
 	{
 		public bool Handles(IMethod method)
 		{
-			return true;
+			return !SD.Debugger.Options.EnableJustMyCode;
 		}
 		
 		public bool IsCompilerGenerated(IMethod method)