include the dropped object type

- 12d75e61 - new thread stack size
- 99e48cb1 - warning text changed
- 6c173324 - default values for BLOBs
- c87e002b - don't return a negative zero

this is useless now, flags are recalculated on load anyway.
But storing flags on disk means we cannot easily change (add,
remove, or renumber) them in the new MariaDB version.

because table->map is set much later.
Use check_vcol_func_processor() to detect fields too.

"thd" is available through the "table" argument, as table->in_use.

Restore the fix from the commit 99cd5a96 that was lost in a merge.

it's not enough to look for NOT NULL IS, this also fails queries like
SELECT NOT NULL <=> NULL;
and adds no value anymore, as the grammar now requires parentheses

* remove a confusing method name - Field::set_default_expression()
* remove handler::register_columns_for_write()
* rename stuff
* add asserts
* remove unlikely unlikely
* remove redundant if() conditions
* fix mark_unsupported_function() to report the most important violation
* don't scan vfield list for default values (vfields don't have defaults)
* move handling for DROP CONSTRAINT IF EXIST where it belongs
* don't protect engines from Alter_inplace_info::ALTER_ADD_CONSTRAINT
* comments

make it return same errors on CREATE as

CREATE ... ( ... DEFAULT const ... )

the error should be "subselect is not allowed here", same as for
DEFAULT ((SELECT 1))

and remove all related casts to uchar*
also remove a couple of unused methods

collaterals:
* use %`s, not '%s'
* use correct SQLSTATE codes for these two errors

- Adding SHOW CREATE TABLE into all DEFAULT tests,
  to cover need_parentheses_in_default() for all items
- Fixing a few items not to print parentheses in DEFAULT:
  spatial function-alike predicates, IS_IPV4 and IS_IPV6 functions,
  COLUMN_CHECK() and COLUMN_EXISTS().

(a new rule in sql_yacc.yy)

- Force usage of () around complex DEFAULT expressions
- Give error if DEFAULT expression contains invalid characters
- Don't use const_charset_conversion for stored Item_func_sysconf expressions
  as the result is not constaint over different executions
- Fixed Item_func_user() to not store calculated value in str_value

ENCRYPT(), SHA(), SHA2(),
AES_ENCRYPT(), AES_DECRYPT(),
DES_ENCRYPT(), DES_DECRYPT()

CRC32(), MD5(), FROM_BASE64(), TO_BASE64(), HEX(), UNHEX(),
ENCODE(), DECODE(), PASSWORD(),
COMPRESS(), UNCOMPRESS(), UNCOMPRESSED_LENGTH().

UUID(), UUID_SHORT()

Miscelaneous functions:
BENCHMARK(), SLEEP(), ROW_COUNT(), FOUND_ROWS(),
GET_LOCK(), RELEASE_LOCK(), IS_USED_LOCK(), IS_FREE_LOCK(),
MASTER_POS_WAIT(), MASTER_GTID_WAIT(), BINLOG_GTID_POS(),
ST_GIS_DEBUG(), DECODE_HISTOGRAM(),

Miscelaneous functions:
LIKE_RANGE_MIN(), LIKE_RANGE_MAX(), WEIGHT_STRING(),
GET_FORMAT(), FORMAT(), LOAD_FILE().

Metadata functions

Dynamic column functions

Functions DATABASE() and USER().