Problem: Tables without PK can cause performance problems on the slave
when doing row-based replication.

Solution: Add a system variable sql_require_primary_key (global &
session), which if set, causes CREATE or ALTER statements that would
yield a table without PK, to fail with ER_TABLE_WITHOUT_PK

Add a binlog event to propagate the setting of this variable to the
slave, so that the slave applier will be able to follow the
master. The original setting remains in effect for normal connections.

Change-Id: Ide65c39a11c4fd6ddf5c450142450c13321e3f1f