* symtab.h (struct symtab) <includes, user>: New fields.

	* block.h (struct block_iterator) <d, idx, which>: New fields.
	* block.c (initialize_block_iterator, find_iterator_symtab)
	(block_iterator_step, block_iter_name_step)
	(block_iter_match_step): New functions.
	(block_iterator_first, block_iterator_next)
	(block_iter_name_first, block_iter_name_next)
	(block_iter_match_first, block_iter_match_next): Rewrite.
	(get_block_symtab): New function.