* class.c (dfs_modify_vtables): Simplify condition. Return
	dfs_skip_bases as appropriate.
	(modify_all_vtables): Walk in pre-order.
	* search.c (dfs_walk_all, dfs_walk_once_r,
	dfs_walk_once_accessible_r): Assert post order function never
	returns dfs_skip_bases.

From-SVN: r88939