Include mtext.h.

Include mtext.h.
(linebreak_table, M_break_at_space, M_break_at_word)
(M_break_at_any, M_kinsoku_bol, M_kinsoku_eol): New variables.
(compose_glyph_string): Check POS before getting Mface text
property.
(truncate_gstring): Give correct TO arg to line_break function.
(GET_LB_TYPE): New macro.
(find_break_backward, find_break_forward): New functions.
(mdraw__init): Initialize the above new variables.
(mdraw__fini): Free linebreak_table.
(mdraw_default_line_break): Use find_break_backward and
find_break_forward.