API instead.
This is a pre-requisite of the fix for Bug 12713, which changes the
data type of thd->ha_data from void * to struct Ha_data.


include/mysql/plugin.h:
  Provide accessors to thd->ha_data for simple and robust code.
sql/ha_ndbcluster_binlog.h:
  Use getters/setters of thd->ha_data, instead of direct access.
sql/handler.cc:
  Use a getter of thd->ha_data instead of direct access.
sql/log.cc:
  Use getters/setters of thd->ha_data, instead of direct access.
sql/rpl_utility.h:
  Fix a compilation warning (declaration order must match initialization
  order in constructor).
storage/federated/ha_federated.cc:
  Use interface accessors to thd->ha_data, instead of direct access.