When a table is being updated it has two set of fields - fields required for
checks of conditions and fields to be updated. A storage engine is allowed
not to retrieve columns marked for update. Due to this fact records can't
be compared to see whether the data has been changed or not. This makes the
server always update records independently of data change.

Now when an auto-updatable timestamp field is present and server sees that
a table handle isn't going to retrieve write-only fields then all of such
fields are marked as to be read to force the handler to retrieve them.


mysql-test/r/innodb_mysql.result:
  Added a test case for the bug#29310: An InnoDB table was updated when the data wasn't actually changed.
mysql-test/include/mix1.inc:
  Added a test case for the bug#29310: An InnoDB table was updated when the data wasn't actually changed.
sql/sql_update.cc:
  Bug#29310: An InnoDB table was updated when the data wasn't actually changed.
  Now the mysql_update function when an auto-updatable timestamp field is
  present marks write-only fields as to be read to force the table handler
  to retrieve them.
sql/sql_insert.cc:
  Bug#29310: An InnoDB table was updated when the data wasn't actually changed.
  Now the write_record function can compare records when fileds to be written is
  a subset of the fields to be read while updating a record.