Misc changes:
- fix for benign Valgrind error, compiler warnings
- fix for a segfault in execution of maria_delete_all_rows() and one
when taking multiple checkpoints
- fix for too paranoid assertion
- adding ability to take checkpoints at the end of the REDO phase
and at the end of recovery.
- other minor changes


storage/maria/ha_maria.cc:
  The checkpoint done after Recovery is finished, is moved to
  maria_recover().
storage/maria/ma_bitmap.c:
  fix for Valgrind error: the "shadow debug copy" of the bitmap page
  started unitialized and so ma_print_bitmap() would use it uninitialized
storage/maria/ma_checkpoint.c:
  * reset pointers to NULL after freeing them, or we segfault at
  next checkpoint in my_realloc().
  * fix for compiler warnings.
storage/maria/ma_delete_all.c:
  info->trn is NULL for non-transactional tables
storage/maria/ma_locking.c:
  correct assertion (it fired wrongly in execution of REDO_DROP_TABLE
  due to the maria_extra(HA_PREPARE_FOR_DROP)->_ma_decrement_open_count()
  ->maria_lock_database(F_UNLCK); another solution would have been to
  not call _ma_decrement_open_count() (it's ok to have a wrong open
  count in a table which we are dropping), but the same problem
  would still exist for REDO_RENAME_TABLE.
storage/maria/ma_loghandler.c:
  fail early if UNRECOVERABLE_ERROR
storage/maria/ma_recovery.c:
  * new argument to maria_apply_log(): should it take checkpoints
  (at end of REDO phase and at the very end) or no.
  * moving the call to translog_next_LSN() into
  parse_checkpoint_record() ("hide the details").
  * Refining an error detection for something which could happen
  if there is a checkpoint record in the log.
  * Using close_one_table() instead of maria_extra(HA_EXTRA_PREPARE_FOR_DROP|RENAME),
  as it looks safer, and also changing how close_one_table() works:
  it now limits itself to scanning all_tables[], thus having one loopp
  instead of two, which should be faster (as a result, it does not
  close tables not registered in this array, which is ok as there
  should not be any).
storage/maria/ma_recovery.h:
  new parameter
storage/maria/maria_read_log.c:
  update to new prototype