title: TabControl Editor(TextBox) - TreeView Issue
body: <p>I'm using C# ICSharpCode.TextEditor and I'm having a slight issue with, when I double click a method on the side in my TreeView box, the text should show up where you're selecting, not at the end of the line.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>private void solutionBox_DoubleClick(object sender, EventArgs e)
  {
      TextEditorControl editor = ActiveEditor;
      if (solutionBox.SelectedNode.Text == "AddAura")
      {
          editor.Text += "Add()";
      }
  }
  </code></pre>
  
  <p>Now that would go to the end of my custom code in the textbox editor:</p>
  
  <pre><code> function Hello(pThis)
       pThis:
   endAdd()
  </code></pre>
  
  <p>So, what I want is when you're beside of 'pThis' and when you double click 'Add()', it will show up beside of 'pThis' &amp; not trying to find the end of the line in the TextBox.</p>
  
  <p>I know '+=' is causing it, but I'd like some more options from other people.</p>