CONSTRAINT

Analysis
========
ALTER TABLE operation on a table with FOREIGN KEY CASCADE
constraint while a concurrent DML operation is being
performed on the table referenced may break the referential
integrity.

In the case of ALTER TABLE operation using COPY algorithm:
a) The ALTER TABLE operation on the table with FOREIGN KEY
   CASCADE constraint, the data is copied from the original
   file to temp file and transaction is committed releasing
   InnoDB locks (also, as an optimization, InnoDB commits
   transaction and releases locks every time ALTER TABLE
   copies 10000 rows).
b) Concurrently if DELETE operation is executed on the
   referenced table, it will trigger delete of records
   on the table being altered. This will end up deleting
   records from the original file since the rename of
   the temp file has not yet completed and locks on the
   original file are not held.
c) The ALTER TABLE operation continues, renaming the temp
   file to the original file leaving behind orphaned rows.

In the case of ALTER TABLE operation using INPLACE algorithm:
a) The DELETE operation on the referenced table acquires an
   LOCK_IS on the table being altered due to the CASCADE
   FOREIGN KEY constraint.
b) The ALTER TABLE operation tries to acquire LOCK_X during
   the commit phase of INPLACE alter and is added to the
   waiting queue since LOCK_IS is acquired by DELETE.
c) DELETE operation upon finding the record to delete, tries
   to acquire LOCK_IX on the table and is added to the wait
   queue. This results in a deadlock with ALTER operation
   being rolled back.
Fix:
====
a) INNODB has introduced a new handler API
   'get_cascade_foreign_key_table_list()' which returns a full
   closure of all tables ordered by the dependency on FOREIGN
   KEY CASCADE constraint.
b) A function called 'lock_fk_dependent_tables()' is added
   which locks the list of tables ordered by the FOREIGN
   KEY CASCADE constraint for the table being altered.
   It is invoked in two places.
   1) Before the copy of data is invoked for the ALTER TABLE,
      COPY algorithm.
   2) Before ALTER TABLE, INPLACE commit.
This avoids the orphaned rows and deadlock.

Please note that this is a temporary workaround which is
necessary until WL#6049 "Meta-data locking for FOREIGN KEY tables"
is implemented

NOTE: Some of the test cases have been removed, since the condition
of concurrent DDL/DML operation on a parent table while a DDL
operation is performed on the the child table having a CASCADE
foreign key constraint is restricted with this patch