This patch fixes two problems that may arise when changing the
value of wsrep_slave_threads:

1) Threads may be leaked if wsrep_slave_threads is changed
   repeatedly. Specifically, when changing the number of slave
   threads, we keep track of wsrep_slave_count_change, the
   number of slaves to start / stop. The problem arises when
   wsrep_slave_count_change is updated before slaves had a
   chance to exit (threads may take some time to exit, as they
   exit only after commiting one more replication event).
   The fix is to update wsrep_slave_count_change such that it
   reflects the number of threads that already exited or are
   scheduled to exit.

2) Attempting to set out of range value for wsrep_slave_threads
   (below 1 / above 512) results in wsrep_slave_count_change to
   be computed based on the out of range value, even though a
   warning is generated and wsrep_slave_threads is set to a
   truncated value. wsrep_slave_count_change is computed in
   wsrep_slave_threads_check(), which is called before mysql
   checks for valid range. Fix is to update wsrep_count_change
   whenever wsrep_slave_threads is updated with a valid value.

Applier does not reset thd->wsrep_apply_toi if applier thread decides
to exit by setting 'exit= true'. The problem is that galera side may
decide not to kill the applier thread: for instance if we try to
SET wsrep_slave_threads = 0; then galera refuses to kill the last
applier thread. If this happens we are left with a thd which has not
been reset to the initial state.
This patch ensures that the thd is reset regardless of the applier
thread exiting or not.

Problem was that 4k page size is not really supported in
Galera. For reference see:
	codership/galera#398

Page size 4k is problematic because WSREP XID info location
that was set to constant UNIV_PAGE_SIZE - 3500 and that is conflicting
with rseg undo slots location if there is lot of undo tablespaces.
Undo tablespace identifiers and page numbers require
at least 126*8=1024 bytes starting from offset 56. Therefore,
WSREP XID startig from offset 596 would overwrite several
space_id,page_no pairs starting from 72th undo log tablespace
space_id,page_no pair at offset 594.
This will cause InnoDB startup failure seen as
[ERROR] InnoDB: Unable to open undo tablespace './undo30579'.

Originally, the undo tablespace ID would always be between
0 and 127. Starting with MySQL 5.6.36 which introduced
Bug #25551311 BACKPORT BUG #23517560 REMOVE SPACE_ID RESTRICTION
FOR UNDO TABLESPACES (merged to MariaDB 10.0.31)
it is possible for an undo tablespace ID to be 0x7773. But in
this case, the page number should be 3, not 0x72650003.
This is just the first collision. The WSREP XID data would
overwrite subsequent slots.

trx0sys.h

trx0sys.cc
	Code formatting and add comments.

Includes Percona XtraDB and TokuDB 5.6.36-82.1

We need to pull rpl config files from MySQL before these tests can be
run.

Problem was a memory overflow in MRR

Reviewed by Sergei Petruna. Testcase by Elena

Squash all connect/10.0's commits into one and keep only
changes from storage/connect directory.

Fix storage_engine test results

MDEV-9739 Assertion `m_status == DA_ERROR || m_status == DA_OK' failed in Diagnostics_area::message() ; connect.xml* tests fail in buildbot

remove ~15 years old print_lock_error() function, use
handler::print_error() instead

Backport from 10.1

        Test fixed for IA64.

        Calculation of the polygon's centroid fixed.

Following merge from 5.6.36, this merge also rejects changes that
collided with the rejection of 6ca4f693c1ce472e2b1bf7392607c2d1124b4293.

We initially rejected 6ca4f693c1ce472e2b1bf7392607c2d1124b4293 because
it was introducing a new storage engine API method.

One query was removed due to inconsistent behaviour with subquery cache
enabled vs disabled. MDEV-13399 has been created to track this change
and fix.

slave_skip_counter must not be reset to 0 during purge_relay_logs. See
MDEV-4937 as to when this change happened.