This patch changes the main name of 3 byte character set from utf8 to
utf8mb3. New old_mode UTF8_IS_UTF8MB3 is added and set TRUE by default,
so that utf8 would mean utf8mb3. If not set, utf8 would mean utf8mb4.
- CREATE TABLE ... SELECT drops constraints for columns that
are both in the create and select part.
- Fixed by copying the constraint in
Column_definiton::redefine_stage1_common()
- If one has both a default expression and check constraint for a
column, one can get the error "Expression for field `a` is refering
to uninitialized field `a`.
- Fixed by ignoring default expressions for current column when checking
for CHECK constraint
