MDEV-7563 Support CHECK constraint as in (or close to) SQL Standard

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

include/mysql_com.h

@@ -158,8 +158,6 @@ enum enum_server_command
 #define FIELD_FLAGS_COLUMN_FORMAT 24    /* Field column format, bit 24-25 */
 #define FIELD_FLAGS_COLUMN_FORMAT_MASK (3 << FIELD_FLAGS_COLUMN_FORMAT)
 #define FIELD_IS_DROPPED (1<< 26)       /* Intern: Field is being dropped */
-#define HAS_EXPLICIT_VALUE (1 << 27)    /* An INSERT/UPDATE operation supplied
-                                          an explicit default value */
 
 #define REFRESH_GRANT           (1ULL << 0)  /* Refresh grant tables */
 #define REFRESH_LOG             (1ULL << 1)  /* Start on new log file */