Bug#13523839 ASSERTION FAILURES ON COMPRESSED INNODB TABLES
btr_cur_optimistic_insert(): Remove a bogus assertion. The insert may
fail after reorganizing the page.
btr_cur_optimistic_update(): Do not attempt to reorganize compressed pages,
because compression may fail after reorganization.
page_copy_rec_list_start(): Use page_rec_get_nth() to restore to the
ret_pos, which may also be the page infimum.
rb:1221