Before MySQL 4.0.18, user-specified constraint names were ignored.
Starting with MySQL 4.0.18, the specified constraint name was
prepended with the schema name and '/'. Now we are transforming
into a format where the constraint name is prepended with the
dict_table_t::name and the impossible UTF-8 sequence 0xff.
Generated constraint names will be ASCII decimal numbers.
On upgrade, old FOREIGN KEY constraint names will be displayed
without any schema name prefix. They will be updated to the new
format on DDL operations.
dict_foreign_t::sql_id(): Return the SQL constraint name
without any schemaname/tablename\377 or schemaname/ prefix.
row_rename_table_for_mysql(), dict_table_rename_in_cache():
Simplify the logic: Just rename constraints to the new format.
dict_table_get_foreign_id(): Replaces dict_table_get_highest_foreign_id().
innobase_get_foreign_key_info(): Let my_error() refer to erroneous
anonymous constraints as "(null)".
row_delete_constraint(): Try to drop all 3 constraint name variants.
Reviewed by: Thirunarayanan Balathandayuthapani
Tested by: Matthias Leich
mysql_prepare_alter_table(): Alter table should check whether
foreign key exists when it expected to exists and
report the error in early stage
dict_foreign_parse_drop_constraints(): Don't throw error if the
foreign key constraints doesn't exist when if exists is given
in the statement.
