The problem is that AFTER UPDATE triggers will fire only if the
new data is different from the old data on the row. The trigger
should fire regardless of whether there are changes to the data.

The solution is to fire the trigger on UPDATE even if there are
no changes to the value (because the value is the same).


mysql-test/r/trigger.result:
  Add test case result for Bug#23771
mysql-test/t/trigger.test:
  Add test case for Bug#23771
sql/sql_update.cc:
  Move the invocation of the after update trigger so that
  the trigger will fire even if the records are the same.