Makefile.in: Refine dependencies.

	* Makefile.in: Refine dependencies.
	* c-opts.c (c_common_handle_option): Do nothing for -Wimport.
	* c.opt: Update help for -Wimport.
	* cppfiles.c: Include hashtab.h.  Update comments.
	(stack_file): Read the file before updating dependencies.
	(once_only_file_p): Be smarter about marking once-only files.
	(_cpp_mark_file_once_only): Correct the check for existence on
	the list.
	(open_file_failed): Use name not path, which is NULL.
	* cpphash.h: Don't include hashtab.h.
	(struct _cpp_file): Remove.
	(struct cpp_reader): Update.
	* cppinit.c (cpp_create_reader): Don't initialize warn_import.
	* cpplib.h (struct cpp_options): Remove warn_import.
	(cpp_simplify_path): Remove.

From-SVN: r70045