Patch #9

Also: Some tests failed in debug mode due to some DBUG_PRINT in the
range optimizer.
Fix: check _db_enabled_() before doing any tree traversal

To repeat:
./mtr --charset-for-testdb=utf8mb4 --defaults-file=include/utf8mb4_my.cnf

locking_part

innodb_icp
innodb_icp_all
innodb_icp_none
myisam_icp
myisam_icp_all
myisam_icp_none

optimizer_bug12837084

subselect_innodb.test

select_all
select_all_bka
select_all_bka_nixbnl
select_icp_mrr
select_icp_mrr_bka
select_icp_mrr_bka_nixbnl
select_none
select_none_bka
select_none_bka_nixbnl

Change-Id: I480fac2801e4135aa6d06c9ee8eb86d3f1f935d8