redefining trigger
      
The 'table->auto_increment_field_not_null' flag is only valid within
processing of a single row, and should be set to FALSE before
navigating to the next row, or exiting the operation.
      
This bug was caused by an SQL error occuring while executing a trigger
after the flag had been set, so the normal resetting was bypassed.
The table object was then returned to the table share's cache in
a dirty condition.   When the table object was reused, an assert
caught that the flag was set.
      
This patch explicitly clears the flag on error/abort.


Backported from mysql-6.0-codebase  revid: 2617.52.1