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().

INET4/INET6 functions

- INT result functions
- CAST variants: COLLATE, BINARY, CONVERT(..USING)

UDF

Numeric functions with string input

Boolean predicates

XML functions

Adding tests for cast, bit functions, string functions.

GIS functions

Testing non-ASCII string literals.

- real functions
- temporal functions
- hybrid functions

MDEV-10134 Add full support for DEFAULT

- Added support for using tables with MySQL 5.7 virtual fields,
  including MySQL 5.7 syntax
- Better error messages also for old cases
- CREATE ... SELECT now also updates timestamp columns
- Blob can now have default values
- Added new system variable "check_constraint_checks", to turn of
  CHECK constraint checking if needed.
- Removed some engine independent tests in suite vcol to only test myisam
- Moved some tests from 'include' to 't'. Should some day be done for all tests.
- FRM version increased to 11 if one uses virtual fields or constraints
- Changed to use a bitmap to check if a field has got a value, instead of
  setting HAS_EXPLICIT_VALUE bit in field flags
- Expressions can now be up to 65K in total
- Ensure we are not refering to uninitialized fields when handling virtual fields or defaults
- Changed check_vcol_func_processor() to return a bitmap of used types
- Had to change some functions that calculated cached value in fix_fields to do
  this in val() or getdate() instead.
- store_now_in_TIME() now takes a THD argument
- fill_record() now updates default values
- Add a lookahead for NOT NULL, to be able to handle DEFAULT 1+1 NOT NULL
- Automatically generate a name for constraints that doesn't have a name
- Added support for ALTER TABLE DROP CONSTRAINT
- Ensure that partition functions register virtual fields used. This fixes
  some bugs when using virtual fields in a partitioning function

use Item->neg to convert generate negative Item_num's
instead of Item_func_neg(Item_num).

Based on the following commit:

  Author: Monty <monty@mariadb.org>
  Date:   Mon May 30 22:44:00 2016 +0300

    Make negative number their own token
    The negation (-) operator will call Item->neg() one underlying numeric constants
    and remove itself (like the NOT() function does today for other NOT functions.

    This simplifies things
    - -1 is not anymore an expression but a basic_const_item
      - improves optimizer
      - DEFAULT -1 doesn't need special handling anymore
      - When we add DEFAULT expressions, -1 will be treated exactly like 1
    - printing of items doesn't anymore put braces around all negative numbers

    Other things fixed:
    - Fixed that longlong converted to decimal's has a more appropriate size
    - Fixed that "-0.0" read into a decimal is interpreted as 0.0

Fixed some test for future when DELETE will not trigger row based replication

Print default values for BLOB's.
This is a part commit for automatic changes to make the real commit smaller.
All changes here are related to that we now print DEFAULT NULL for blob and
text fields, like we do for all other fields.

of bugs easier (MDEV-8919, MDEV-10304, MDEV-10305, MDEV-10307)

- Adding Item::push_note_converted_to_negative_complement() and
  Item::push_note_converted_to_positive_complement()
- Adding virtual methods Item::val_int_signed_typecast() and
  Item::val_int_unsigned_typecast()
- Moving COLUMN_GET() related code from
  Item_func_signed::val_int() and Item_func_unsigned::val_int() to
  Item_dyncol_get::val_int_signed_typecast() and
  Item_dyncol_get::val_int_unsigned_typecast()
- Moving Item_func_signed::val_int_from_str() to Item::val_int_from_str()
  and changing it to get the value from "this" instead of args[0].

The patch does not change behaviour. It's only to simplify fixing of the
mentioned bugs. It will also simplify switching the CAST related code to
use the type handler infrastructure easier (soon).

Result file in engines/funcs test suite needs to be updated accordingly