Include charset.h.

Include charset.h.
(Fchar_to_string, Fstring_to_char): Handle multibyte characters.
(Fsref): New function.
(Fgoto_char): Force point to be at a character boundary.
(Ffollowing_char, Fpreceding_char): Handle multibyte characters.
(Fchar_after): Handle multibyte characters.
(Fchar_before): New function.
(general_insert_function): New function.
(Finsert, Finsert_and_inherit, Finsert_before_markers): Use it.
(Finsert_char): Doc-string refer to markers of
before-insertion-type. Handle multibyte characters.
(Fsubst_char_in_region): Handle multibyte characters.
(Fchar_equal): Don't consider `case' of multibyte characters.
(syms_of_editfns): Handle the new function `char-before'.