Handle string length as size_t, consistently (almost always:))
Change function prototypes to accept size_t, where in the past
ulong or uint were used. change local/member variables to size_t
when appropriate.
This fix excludes rocksdb, spider,spider, sphinx and connect for now.
in JOIN::inject_best_splitting_cond
The value of SplM_opt_info::last_plan should be set to NULL
before any search for a splitting plan for a splittable
materialized table.
Do not try to apply the splitting optimization to a materialized
derived if it's specified by a select with impossible where
or if all joined tables of this select are constant.
