Completed initial debugging and testing of reimplemented cursor motion.

Completed initial debugging and testing of reimplemented cursor motion.

 .gdbinit (prowlims): Display row->minpos and row->maxpos.
 Display truncated_on_left_p and truncated_on_right_p flags.
 Formatting fixes.
 (pmtxrows): Display the ordinal number of each row.  Don't display
 rows beyond the last one.
 xdisp.c (RECORD_MAX_MIN_POS): New macro.
 (display_line): Use it to record the minimum and maximum buffer
 positions for glyphs in the row being assembled.  If word wrap is
 in effect, restore minimum and maximum positions seen up to the
 wrap point, when iterator returns to it.
 (find_row_edges): Fix logic; eol_pos should be tested before the
 rest.
 (try_window_reusing_current_matrix): Give up if in bidi-reordered
 row and cursor not already at point.  Restore original pre-bidi
 code for unidirectional buffers.
 bidi.c (bidi_cache_shrink, bidi_cache_iterator_state): Fix
 reallocation of the cache.  (Bug#6210)
 (bidi_cache_iterator_state): Don't zero out new_paragraph (it is
 not copied by bidi_copy_it).