mariadb10: use thd->abort_on_warning
mariadb10: use thd->abort_on_warning

Because thd_kill_level(thd) doesn't reflect strict
mode (STRICT_TRANS_TABLES).

I don't know why b3db89c2b99f802fbc6e7798d1e0f14f58d36ee9 was applied.

mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga,mroonga/mroonga,mroonga/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga