Analysis
--------
When an ALTER TABLE operation is performed with an invalid foreign key
constraint, the error reported is ER_CANT_CREATE_TABLE(Cannot create
the table). The ALTER TABLE operation is performed on a copy of the
original table, the original table is later deleted and the copy is
renamed to the original table name. The error reported contains the
temporary table name which is of the format
'database_ name.#sql-[0-9_a-f-]*'.

Fix:
---
print_error() which maps the handler error to a SQL error has been used
to report the error. This has helped in reporting more specific errors
instead of the previously reported generic error ER_CANT_CREATE_TABLE
(Cannot create the table) in most of the error scenarios. For the case
of invalid foreign key constraint, the error that will be reported is:
ER_CANNOT_ADD_FOREIGN- Cannot add foreign key constraint.