SQL_MODE was ignored when a client issued INSERT DELAYED.

Some system settings weren't copied as intended when a record was saved for
a delayed insert. 


mysql-test/r/delayed.result:
  Added test case
mysql-test/t/delayed.test:
  Added test case
sql/sql_insert.cc:
  - Added two new variables (sql_mode, auto_increment_field_not_null) to support
    SQL_MODE in INSERT DELAYED statements.