BLOB whose size didn't change. Fix for probably impossible problem
in Recovery.


mysql-test/r/maria.result:
  result for new test
mysql-test/t/maria.test:
  testcase for a bug (used to segfault)
storage/maria/ma_blockrec.c:
  When writing a record, we put BLOBs into the head part if there is
  room for them. "Is there room" was first decided by
  !(tmp_data + length > end_of_data) (line 1894)
  but then was tested again as
  *blob_lengths < (ulong)(end_of_data - data). We see that in case of
  equality, the first condition was true but the second was not,
  so it was inconsistent and crashed later.
storage/maria/ma_recovery.c:
  When wondering if recovery should update the state (like state.records):
  if table was closed, its is_of_horizon was set to X, then
  table was reopened and a REDO was written. If this REDO had LSN
  X (as horizon is just a lower bound of the LSN of the next record),
  we have to apply it. In practice this equality probably could not
  happen because of LOGREC_FILE_ID would be written before the REDO.