After dumping triggers mysqldump copied 
the value of the OLD_SQL_MODE variable to the SQL_MODE
variable. If the --compact option of the mysqldump was
not set the OLD_SQL_MODE variable had the value
of the uninitialized SQL_MODE variable. So
usually the NO_AUTO_VALUE_ON_ZERO option of the
SQL_MODE variable was discarded.

This fix is for non-"--compact" mode of the mysqldump,
because mysqldump --compact never set SQL_MODE to the
value of NO_AUTO_VALUE_ON_ZERO.

The dump_triggers_for_table function has been modified
to restore previous value of the SQL_MODE variable after
dumping triggers using the SAVE_SQL_MODE temporary
variable.


client/mysqldump.c:
  Fixed bug #29788.
  The dump_triggers_for_table function has been modified
  to restore previous value of the SQL_MODE variable after
  dumping triggers using the SAVE_SQL_MODE temporary
  variable.
mysql-test/r/mysqldump.result:
  Updated test case for bug #29788.
mysql-test/t/mysqldump.test:
  Updated test case for bug #29788.