In some places, the wrong icon is being used as a trash icon, as the stock delete icons in GTK+ are trash cans, but this is not true in all themes. The attached patches fixes the UI to do the following:

Remove the undelete icon from the menu item (it is not in the toolbar)
Update several icons that were using GTK_STOCK_DELETE to use the gnome trash icons

We probably should also change "Delete" to "Move to Trash" in the menus, but I think this can wait, as it breaks string freeze. However, doing this will improve the consistency with Nautilus, and also more directly show the behavior of deleting mail. Delete Folder should still use the delete icon, as it is actually non-recoverable.