Fix int/EMACS_INT use in casefiddle.c and syntax.c.

Fix int/EMACS_INT use in casefiddle.c and syntax.c.

 syntax.c (scan_words, update_syntax_table)
 (prev_char_comend_first, back_comment, skip_chars)
 (skip_syntaxes, Fforward_comment, Fbackward_prefix_chars): Use
 EMACS_INT for buffer and string positions.
 syntax.h (scan_words, update_syntax_table): Adjust prototypes.
 casefiddle.c (operate_on_word): Use EMACS_INT for buffer
 positions.