(scan_sexps_forward): Additional arg FROM_BYTE. Calls changed.

(scan_sexps_forward): Additional arg FROM_BYTE.  Calls changed.
(find_defun_start): Additional arg POS_BYTE.
Save final byte pos in find_start_value_byte.
(find_start_value_byte): New variable.

(Fforward_comment): Scan by bytes and chars.
(Fbackward_prefix_chars): Scan by bytes and chars.
(scan_words, scan_sexps_forward): Scan bytes as well as chars.
(skip_chars, scan_lists): Scan by bytes and chars.  Now static.

(char_quoted): Take charpos and bytepos as args.
(back_comment): Likewise.
(update_syntax_table): Arg renamed.
(inc_bytepos, dec_bytepos): New functions.