UPDATE if the row wasn't actually changed.

This bug was caused by fix for bug#19978. It causes AFTER UPDATE triggers
not firing if a row wasn't actually changed by the update part of the
INSERT .. ON DUPLICATE KEY UPDATE.

Now triggers are always fired if a row is touched by the INSERT ... ON
DUPLICATE KEY UPDATE.


sql/sql_insert.cc:
  Bug#27006: AFTER UPDATE triggers not fired with INSERT ... ON DUPLICATE KEY
  UPDATE if the row wasn't actually changed.
  Now triggers are always fired if a row is touched by the INSERT ... ON
  DUPLICATE KEY UPDATE.
mysql-test/r/trigger.result:
  Added a test case for the bug#27006: AFTER UPDATE triggers not fired with INSERT ... ON DUPLICATE KEY
  UPDATE if the row wasn't actually changed.
mysql-test/t/trigger.test:
  Added a test case for the bug#27006: AFTER UPDATE triggers not fired with INSERT ... ON DUPLICATE KEY
  UPDATE if the row wasn't actually changed.