Aria temporary tables account allocated memory as specific to the current
THD. But this fails for slave threads, where the temporary tables need to be
detached from any specific THD.

Introduce a new flag to mark temporary tables in replication as "global",
and use that inside Aria to not account memory allocations as thread
specific for such tables.

Based on original suggestion by Monty.
Reviewed-by: Monty <monty@mariadb.org>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>