The event scheduler has a THD which is used for e.g. keeping track
of the timing of the events. Thus, each scheduling of an event will
make use of this THD, which in turn allocates memory in the THD's
mem root. However, the mem root was never cleared, and hence, the
memory occupied would monotonically increase throughout the life
time of the server.

The root cause was found by Jon Olav Hauglid, and this fix clears the
THD's mem root for each event being scheduled.

Change-Id: I462d2b9fd9658c9f33ab5080f7cd0e0ea28382df

* Update wrong zip-code

Applied lost in a merge revision 7f38a07:

MDEV-10043 - main.events_restart fails sporadically in buildbot (crashes upon
             shutdown)

There was race condition between shutdown thread and event worker threads.

Shutdown thread waits for thread_count to become 0 in close_connections(). It
may happen so that event worker thread was started but didn't increment
thread_count by this time. In this case shutdown thread may miss wait for this
working thread and continue deinitialization. Worker thread in turn may continue
execution and crash on deinitialized data.

Fixed by incrementing thread_count before thread is actually created like it is
done for connection threads.

Also let event scheduler not to inc/dec running threads counter for symmetry
with other "service" threads.

             shutdown)

There was race condition between shutdown thread and event worker threads.

Shutdown thread waits for thread_count to become 0 in close_connections(). It
may happen so that event worker thread was started but didn't increment
thread_count by this time. In this case shutdown thread may miss wait for this
working thread and continue deinitialization. Worker thread in turn may continue
execution and crash on deinitialized data.

Fixed by incrementing thread_count before thread is actually created like it is
done for connection threads.

Also let event scheduler not to inc/dec running threads counter for symmetry
with other "service" threads.

Part 5: Removing calls to current_thd in net_read calls, creating fields,
        query_cache, acl and some other places where thd was available

including the big commit
  commit 305130361bf72726de220f3d2b2787395e10be61
  Author: Marc Alff <marc.alff@oracle.com>
  Date:   Tue Feb 10 11:31:32 2015 +0100

      WL#8354 BACKPORT DIGEST IMPROVEMENTS TO MYSQL 5.6

(with the following commits) and related changes in sql/