PR debug/33739
	* gfortran.h (gfc_file): Remove included_by field, add sibling and
	down.
	(gfc_start_source_files, gfc_end_source_files): New prototypes.
	* parse.c (gfc_parse_file): Call gfc_start_source_files and
	gfc_end_source_files instead of calling the debugging hooks directly.
	* error.c (show_locus): Use up field instead of included_by.
	* scanner.c (change_file, gfc_start_source_files,
	gfc_end_source_files): New functions.
	(gfc_advance_line): Call change_file instead of calling debug hooks
	directly.
	(get_file): Set up rather than included_by.  Initialize down and
	sibling.
	(preprocessor_line, load_file): Don't set up field here.

	* gfortran.dg/debug_2.f: New test.

From-SVN: r130629