This failure was caused because of several bugs:
- Someone had removed s3-slave-ignore-updates=1 from slave.cnf, which
  caused the slave to remove files that the master was working on.
- Bug in ha_partition::change_partitions() that didn't reset m_new_file
  in case of errors. This caused crashes in ha_maria::extra() as the
  maria handler was called on files that was already closed.
- In ma_pagecache there was a bug that when one got a read error one a
  big block (s3 block), it left the flag PCBLOCK_BIG_READ on for the page
  which cased an assert when the page where flushed.
- Flush all cached tables in case of ignored ALTER TABLE

Note that when merging code from 10.3, that fixes the partition bug, use
the code from this patch instead.

Changes to ma_pagecache.cc written or reviewed by Sanja