DROP TABLE now also works on empty or short .frm files

- We don't check constraints when doing delete

Most "new" failures fixed in the following files:
- sql_select.cc
- item.cc
- item_func.cc
- opt_subselect.cc

Other things:
- Allocate udf_handler strings in mem_root
  - Required changes in sql_string.h
- Add mem_root as argument to some new [] calls
- Mark udf_handler strings as thread specific
- Removed some comment blocks with code

Affected tests:
sql_sequence.gtid sql_sequence.replication

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=79887
was fixed in 7.4 and 8.2.

Both of these reached end of life in February 2011
https://www.freebsd.org/releases/Signed-off-by: Daniel Black <daniel@linux.vnet.ibm.com>

Relax a too strict debug assertion, and add a test.

Allow DROP TABLE `#mysql50##sql-...._.` to drop tables that were
being rebuilt by ALGORITHM=INPLACE

NOTE: If the server is killed after the table-rebuilding ALGORITHM=INPLACE
commits inside InnoDB but before the .frm file has been replaced, then
the recovery will involve something else than DROP TABLE.

NOTE: If the server is killed in a true inplace ALTER TABLE commits
inside InnoDB but before the .frm file has been replaced, then we
are really out of luck. To properly handle that situation, we would
need a transactional mysql.ddl_fixup table that directs recovery to
rename or remove files.

prepare_inplace_alter_table_dict(): Use the altered_table->s->table_name
for generating the new_table_name.

table_name_t::part_suffix: The start of the partition name suffix.

table_name_t::dbend(): Return the end of the schema name.

table_name_t::dblen(): Return the length of the schema name, in bytes.

table_name_t::basename(): Return the name without the schema name.

table_name_t::part(): Return the partition name, or NULL if none.

row_drop_table_for_mysql(): Assert for #sql, not #sql-ib.

rec_get_offsets_func(): Relax a bogus debug assertion.
It would fail when we are operating on a copied prefix
of a node pointer record.

row_log_table_apply_op(): Remove references to dict_table_t::n_vcols.
Virtual column information is no longer being written to the log.

row_log_t: Remove the unused fields n_old_col, n_old_vcol.

MDEV-13723: Server crashes in ha_heap::find_unique_row or Assertion `0' failed in st_select_lex_unit::optimize with INTERSECT

With INTERSECT/EXCEPT fact that subquery item of IN/ALL/ANY was not assigned value does not mean that temporary table used for calculating unit is empty (records could be deleted).

When MySQL 5.7 introduced indexed virtual columns, it introduced
several bugs into the online table-rebuilding ALTER, that is,
the row_log_table_apply() family of functions.

The online_log format that was introduced for online table-rebuilding
ALTER in MySQL 5.6 should be sufficient. Ideally, any indexed virtual
column values would be evaluated based on the log records in the temporary
file. There is no need to log virtual column values.

(For ADD INDEX, that is row_log_apply(), we always must log the values of
the keys, no matter if the columns are virtual.)

Because omitting the virtual column values removes any chance of
row_log_table_apply() working with indexed virtual columns, we
will for now refuse LOCK=NONE in table-rebuilding ALTER operations
when indexes on virtual columns exist. This restriction would be
lifted in MDEV-14341.

innobase_indexed_virtual_exist(): New predicate, to determine if
indexed virtual columns exist in a table definition.

ha_innobase::check_if_supported_inplace_alter(): Refuse online rebuild
if indexed virtual columns exist.

rec_get_converted_size_temp_v(), rec_convert_dtuple_to_temp_v(): Remove.

row_log_table_delete(), row_log_table_update(, row_log_table_insert():
Remove parameters for virtual columns.

trx_undo_read_v_rows(): Remove the col_map parameter.

row_log_table_apply(): Do not deal with virtual columns.

Conflicts:
	mysql-test/r/cte_recursive.result
	mysql-test/r/derived_cond_pushdown.result
	mysql-test/t/cte_recursive.test
	mysql-test/t/derived_cond_pushdown.test
	sql/datadict.cc
	sql/handler.cc

MDEV-14333 Mariabackup --apply-log-only crashes if incomplete transactions with update_undo logs are present

trx_undo_free_prepared(): Relax the assertion for
mariabackup --apply-log-only.

MDEV-14164: Unknown column error when adding aggregate to function in oracle style procedure FOR loop

Make differentiation between pullout for merge and pulout of outer field during exists2in transformation.
In last case the field was outer and so we can safely start from name resolution context of the SELECT where it was pulled.
Old behavior lead to inconsistence between list of tables and outer name resolution context (which skips one SELECT for merge purposes) which creates problem vor name resolution.

Recording mtr.add_suppression("Could not use .*")
instead of mtr.add_suppression("Could not open .*")
in tests:
- binlog_encryption.rpl_binlog_errors
- binlog_encryption.binlog_index

There was a problem in the recent patch for MDEV-10817:
get_date() must "return true" on null_value rather than "return 0"

(forgot to fix Item_sum_hybrid::get_date() after copying and pasting
from Item_sum_hybrid::val_str()).

FlushObserver::flush(): Never discard unwritten changes.
We do not want to risk corrupting the system tablespace
or .ibd files that are not part of a table-rebuilding ALTER.

Ever since MDEV-10813 cleaned up InnoDB use of atomic memory operations
and made buf_block_fix() an atomic operation, some conditions around
buf_block_fix() have been unnecessary.

This problem was earlier fixed by the patch for MDEV-8910. Adding tests only.