Mirror continuation indicators for R2L lines; fix face extension on TTY.

Mirror continuation indicators for R2L lines; fix face extension on TTY.

 xdisp.c (extend_face_to_end_of_line): Fix face extension at ZV.
 term.c (produce_special_glyphs): Mirror the backslash
 continuation character in R2L lines.
 xdisp.c (set_cursor_from_row, display_line): Use
 MATRIX_ROW_CONTINUATION_LINE_P instead of testing value of
 row->continuation_lines_width.
 fringe.c (update_window_fringes): For R2L rows, swap the bitmaps
 of continuation indicators on the fringes.