New functions.
(struct file_name_list): New members: name_map, got_name_map.
(main, path_include, do_include, do_once): Set got_name_map.
(do_include): Use open_include_file instead of open.  Add new
parameter to lookup_import calls.
(lookup_import): New parameter searchptr.  Call open_include_file
instead of open.

From-SVN: r6307