Bug #22960 --> fix an inefficiency when deleting a message...we were clearing the

message pane and msg header view overlay twice every time we deleted
a msg...this helps make deleting look faster...The fix is to not
 clear the msg pane every time selection changes in the thread pane..
instead only clear the msg pane when the folder selection changes..

mailnews/base/resources/content/commandglue.js

@@ -415,18 +415,27 @@ function LoadSelectionIntoMessagePane()
 	if ( selArray && (selArray.length == 1) )
 		LoadMessage(selArray[0]);
 	else
-		ClearMessagePane();
+  {
+    // don't necessarily clear the message pane...if you uncomment this,
+    // you'll be introducing a large inefficiency when deleting messages...as deleting
+    // a msg brings us here twice...so we end up clearing the message pane twice for no
+    // good reason...
+		// ClearMessagePane();
+  }
 }
 
 function FolderPaneSelectionChange()
 {
 	var tree = GetFolderTree();
-	
 	if(tree)
 	{
 		var selArray = tree.selectedItems;
 		if ( selArray && (selArray.length == 1) )
+    {
 			ChangeFolderByDOMNode(selArray[0]);
+      // explicitly force the message pane to get cleared when we switch folders
+      ClearMessagePane(); 
+    }
 		else
 		{
 			var threadTree = GetThreadTree();