cppfiles.c: Update comments.

cppfiles.c: Update comments.

        * cppfiles.c: Update comments.
        (_cpp_read_file): Don't check for NULL filenames any more.
        * cppinit.c (cpp_start_read): Don't do canonicalization of
        in_fname and out_fname.  Use the passed file name exclusively.
        (_cpp_handle_options): Don't treat "-" as a command line option,
        but as a normal filename.
        (_cpp_post_options): Canonicalize in_fname and out_fname.
        * cppmain.c (printer_init): Don't check out_fname for NULL.
        * c-lex.c (orig_filename): Rename cpp_filename for clarity.
        (init_c_lex): Update, and use "" to represent stdin to CPP.
        (yyparse): Update.

From-SVN: r39938