Test that
- Fake changes do not cause any InnoDB write whatsoever except for the
  transaction system header page rewrite.
- Fake changes do not cause any InnoDB statistics update.

Add an assert that row_update_statistics_if_needed() is never called
for fake changes.

Fix bug http://bugs.mysql.com/bug.php?id=71761 (ANALYZE TABLE should remove
its table from background stat processing queue) so that ANALYZE TABLE calls
prevent any queued background stats updates which then cause stat table
writes at unpredictable times.

Export trx_sys->max_trx_id as a new InnoDB status variable innodb_max_trx_id.

Extend start|stop_fake_changes.inc to
- quieten InnoDB writes by waiting for purge and cleaners to catch up;
- verify that INFORMATION_SCHEMA.INNODB_SYS_TABLESTATS.MODIFIED_COUNTER is not
  affected by the fake changes;
- verify that Innodb_buffer_pool_write_requests, Innodb_buffer_pool_pages_dirty,
  INFORMATION_SCHEMA.TABLE_STATISTICS.IO_WRITE_REQUESTS, and
  INNODB_PAGES_WRITTEN are not updated more than necessary for the transaction
  system header page rewrite.