by ma_test_recovery.pl when it happens that Recovery does not recreate
pages exactly as they were at first run: this option will help us
verify that the differences are in unimportant page pieces (those pieces
will be zeroed by --zerofill-keep-lsn, but not the important LSNs).


include/myisamchk.h:
  new zerofill flag for maria_chk
storage/maria/ma_check.c:
  If T_ZEROFILL_KEEP_LSN, we don't zero out LSNs of data/index pages.
  Then the table is not movable. We still mark it zerofilled, it helps
  to know what was last done to the table.
storage/maria/maria_chk.c:
  New option --zerofill-keep-lsn