void _modest_header_view_sender_receiver_cell_data (GtkTreeViewColumn *column, GtkCellRenderer *renderer,
GtkTreeModel *tree_model, GtkTreeIter *iter, gboolean is_sender);
void _modest_header_view_compact_header_cell_data (GtkTreeViewColumn *column, GtkCellRenderer *renderer,
GtkTreeModel *tree_model, GtkTreeIter *iter, gpointer user_data);
void _modest_header_view_sender_receiver_cell_data (GtkTreeViewColumn *column, GtkCellRenderer *renderer,
GtkTreeModel *tree_model, GtkTreeIter *iter, gboolean is_sender);
void _modest_header_view_compact_header_cell_data (GtkTreeViewColumn *column, GtkCellRenderer *renderer,
GtkTreeModel *tree_model, GtkTreeIter *iter, gpointer user_data);