(find_realized_face): Return value changed. If RFONT is

(find_realized_face): Return value changed.  If RFONT is
NULL, avoid unnecessary checking.
(free_face): Free face->realized_face_list.
(mface__realize): Adjusted for the change of find_realized_face.
If it returns a realized face that needs update, free it and
realize a new one.  Push a new realized face to
frame->realized_face_list instead of appending.
(mface__for_chars): Adjusted for the change of find_realized_face.
Short cut if the required font is in rface->ascii_rface.
(mface_put_prop): Free old value if necessary.  Set need_update
member of realized faces to 1.