[silverlight] Always scrolling the scroll bar to the bottom of a TextBox

found this at http://www.gamedev.net/community/forums/topic.asp?topic_id=550283

very useful.

// If there is current text and it does not end in a newline, add one. 

if (!string.IsNullOrEmpty(outputWindow.Text) && !outputWindow.Text.EndsWith(Environment.NewLine)) 

{  

outputWindow.Text += Environment.NewLine; 

} 

// Append the text. 

outputWindow.Text += DateTime.Now.ToString(); 

// Set the selection to the end of the text, zero length. 

outputWindow.SelectionLength = 0; 

outputWindow.SelectionStart = outputWindow.Text.Length;