WL #3337 (Event scheduler new architecture)

Cut Nr. 8.

All tests pass.

Separated Event_scheduler into Event_queue and Event_scheduler.
Added new Event_scheduler_ng which is the new scheduler and is used
system-wide. Will be moved to the event_scheduler.cc in the future.
Using Event_timed in Event_queue as well as cloned during execution.
Next step is to have Event_worker_data which will be used during execution
and will take ::compile()/::execute() out of Event_timed.


mysql-test/r/events.result:
  update result
mysql-test/r/events_bugs.result:
  update result
mysql-test/r/ps_1general.result:
  update result
mysql-test/r/skip_name_resolve.result:
  update result
mysql-test/r/sp-threads.result:
  update result
mysql-test/r/sp_notembedded.result:
  update result
mysql-test/r/status.result:
  update result
mysql-test/t/events_stress.test:
  Make event_stress a bit longer
sql/Makefile.am:
  Add new event_scheduler_ng.h/cc . These are only to be in the experimental
  clone. Later their content will be moved to event_scheduler.h/cc
sql/event_data_objects.cc:
  Allocate strings memory on own memory root, instead
  on the schedulers. Thus don't "leak" memory. This should
  fix bug#18683 memory leak in event scheduler
sql/event_data_objects.h:
  add mem_root
  add THD - this is only temporal, will be moved to class Event_job_data
  once Event_job_data is responsible for the execution.
sql/event_db_repository.cc:
  Remove unused code.
  Cosmetic changes
sql/event_queue.cc:
  Now use the Event_scheduler_ng (NextGen)
sql/event_queue.h:
  Now use the Event_scheduler_ng (NextGen)
sql/event_scheduler.cc:
  This file is no more used, but will be soon.
sql/event_scheduler.h:
  This file is no more used but will be soon
sql/events.cc:
  Now use the Event_scheduler_ng (NextGen)
sql/events.h:
  Now use the Event_scheduler_ng (NextGen)
sql/mysqld.cc:
  Make it again possible to kill the scheduler thread
sql/set_var.cc:
  Now use the Event_scheduler_ng (NextGen)
sql/share/errmsg.txt:
  Shorten the message.
sql/sql_show.cc:
  Loading is on a own root, then don't use thd->mem_root

sql/sql_show.cc

@@ -4177,7 +4177,7 @@ copy_event_to_schema_table(THD *thd, TABLE *sch_table, TABLE *event_table)
 
   restore_record(sch_table, s->default_values);
 
-  if (et.load_from_row(thd->mem_root, event_table))
+  if (et.load_from_row(event_table))
   {
     my_error(ER_CANNOT_LOAD_FROM_TABLE, MYF(0));
     DBUG_RETURN(1);