speed up delete mail marked as junk enormously 217299 sr=mscott, a/r=sspitzer

mailnews/base/resources/content/mailCommands.js

@@ -636,6 +636,7 @@ function deleteJunkInFolder()
         // since we will be deleting all selected messages
         treeSelection.clearSelection();
         clearedSelection = true;
+        treeSelection.selectEventsSuppressed = true;
       }
       treeSelection.rangedSelect(i, i, true /* augment */);
     }
@@ -646,6 +647,7 @@ function deleteJunkInFolder()
   if (!clearedSelection)
     return;
 
+  treeSelection.selectEventsSuppressed = false;
   // delete the selected messages
   //
   // XXX todo