Second edition: error message was deleted as Segey suggested
Now name of the constraint will be used as the name of the key
if the last not specified


mysql-test/r/constraints.result:
  appropriate test result
mysql-test/t/constraints.test:
  test case for 1189
sql/sql_yacc.yy:
  language definitions changed so that we can obtaint constraint's name
  and send it as the name of the key if it's not specified