(Fgoto_char): When arg is a marker, copy char and byte

(Fgoto_char): When arg is a marker, copy char and byte
positions from it.  When arg is an integer, no need to worry that it
is in middle of a character.
(buildmark): Take 2 args (charpos and bytepos).  Callers changed.
(Fline_beginning_position): Save and restore both kinds of PT.
(Fprevious_char): Use PT_BYTE.
(Fbolp, Feolp): Use PT_BYTE.
(transpose_markers): Take args in chars and bytes.
(Ftranspose_regions): Work with byte and char positions.
(Fchar_after, Fchar_before): Use bytepos.
(make_buffer_string): Convert charpos to bytepos.
(Fcompare_buffer_substrings): Work with charpos and bytepos.
(Fsubst_char_in_region): Handle charpos and bytepos.
(Fwiden, Fnarrow_to_region): Likewise.
(save_restriction_restore): Update PT and PT_BYTES.
Cast arg to doprnt_lisp.