Word Export: prevent cross-thread exception (#184)

* Word Export: prevent cross-thread exception

Use InvokeRequired and Invoke to re-execute the TextForReal call.

Notes:
- XHTML export is also calling this from a different thread but we
were not seeing this error because the text string was the same
as the current value so no change was made.
- The exception was only happening when there were reversals
and it seemed to only/mostly happen in debug builds.

Src/Common/Controls/FwControls/StatusBarTextBox.cs

@@ -135,6 +135,12 @@ public  string TextForReal
 			{
 				CheckDisposed();
 
+				if (m_bar.InvokeRequired)
+				{
+					m_bar.Invoke((Action<string>)(s => this.TextForReal = s), value);
+					return;
+				}
+
 				m_text = value;
 				// But we still need to set the Text property to get autosizing to work.
 				this.Text = m_text;