normal DROP TABLE with many tables continues after an error,
trying to drop as many tables as possible. But DROP TEMPORARY TABLE
was aborting on the first error. Change it to behave as DROP TABLE does.
truncating a temporary table
TRUNCATE expects only one TABLE instance (which is used by TRUNCATE
itself) to be open. However this requirement wasn't enforced after
"MDEV-5535: Cannot reopen temporary table".
Fixed by closing unused table instances before performing TRUNCATE.
