Don't include Freetype headers. Include "ftfont.h".

Don't include Freetype headers.  Include "ftfont.h".
(struct ftfont_info) [HAVE_LIBOTF]: New members maybe_otf and otf.
(ftfont_open) [HAVE_LIBOTF]: Initialize the above members.
(ftfont_driver) [HAVE_LIBOTF, HAVE_M17N_FLT]: Don't set
font_otf_capability and font_drive_otf, set ftfont_shape.
(ftfont_list): Adjusted for the change of :otf property value.
(struct MFLTFontFT) [HAVE_LIBOTF, HAVE_M17N_FLT]: New struct.
(ftfont_get_glyph_id, ftfont_get_metrics, ftfont_check_otf)
(adjust_anchor, ftfont_drive_otf, ftfont_shape_by_flt)
(ftfont_shape) [HAVE_LIBOTF, HAVE_M17N_FLT]: New function.s
(DEVICE_DELTA) [HAVE_LIBOTF, HAVE_M17N_FLT]: New macro.
(otf_gstring, gstring, m17n_flt_initialized): New variables.