To read histograms for a table, we should check if the allocation of statistics was done or not,
if not done we should not try to read histograms for such a table.

to the patch for MDEV-17605

MDEV-14572: Assertion `! is_set()' failed in Diagnostics_area::set_eof_status upon EXPLAIN UPDATE in PS

Restore EXPAIN flag in SELECT_LEX before execution multi-update by flag in LEX
(the same but in other way made before INSERT/DELETE/SELECT)

Without it, mysql_update() didn't know that there will be EXPLAIN result set and was sending OK at the end of the update, which conflicted with the EOF sent later by EXPLAIN.

The patch for MDEV-18738 fixed this problem. Adding tests only.

copy_if_not_alloced() did not handle situations when
"from" is a constant string pointing to a substring of "to",
so this code part freed "to" but then tried to copy its old (already freed)
content to a new buffer:

  if (to->realloc(from_length))
    return from;
  if ((to->str_length=MY_MIN(from->str_length,from_length)))
    memcpy(to->Ptr,from->Ptr,to->str_length);

Adding a new code piece that catches such constant substrings
and propery reallocs "to" to preserve its important part referenced
by "from".

This problem was earlier fixed, possibly by f8a800be
and is not repeatable in 10.1-10.4 any more. Adding tests only.

if log_warnings > 1.

This makes ER_DBACCESS_DENIED_ERROR handling the same as we do for other
"access denied"

Change error message.

names

Added a call to X509_check_ip_asc() in case server_hostname represents
an IP address.

The fix for MDEV-17064 addressed this problem. Adding tests only.

           depends on uninitialised value

Initialized THD::force_read_stats introduced in the patch for MDEV-17605.
Leaving this field uninitialized in the constructor of the THD class may
trigger reading statistical data that is not needed.

Item_func_group_concat stores values in `tree`, which is often, but not
always the same as `&tree_base`.

move privilege specific part of gis2.test to gis_notembedded.test
and the rest to gis.test

Fixed the assert by making sure that not to use EITS if the column statistics was not allocated.

MDEV-11015 Assertion failed: precision > 0 in decimal_bin_size upon SELECT with DISTINCT, CAST and other functions

Item_func_min_max::fix_length_and_dec() erroneously set max_length
to UINT32_MAX.

Merge notes:
In 10.3 this problem had been fixed earlier.
During merge to 10.3, do a "null merge" in item_func.cc

commit ac275d0b4ad (connect/10.0)
Author: Olivier Bertrand <bertrandop@gmail.com>
Date:   Wed Mar 27 12:46:20 2019 +0100

    Comment out unrecognized command line options: Modified CMakeLists.txt

commit 592f1f75ad6
Author: Olivier Bertrand <bertrandop@gmail.com>
Date:   Tue Mar 26 19:52:33 2019 +0100

    Replace Command not recognized by CMake modified: CMakeLists.txt

commit 00f72199b16
Author: Olivier Bertrand <bertrandop@gmail.com>
Date:   Tue Mar 26 18:15:08 2019 +0100

    - Fix MDEV-15793: Server crash in PlugCloseFile with sql_mode=''
      Fixed by replacing sprinf by snprintf in ShowValue to avoid
      buffer overflow. It nows always use a buffer and returns int.
      modified:   storage/connect/tabdos.cpp
      modified:   storage/connect/tabfmt.cpp
      modified:   storage/connect/value.cpp
      modified:   storage/connect/value.h

    - Fix MDEV-18292: CONNECT Engine JDBC not able to issue
      simple UPDATE statement from trigger or stored procedure
      Was not fixed when the same table was called several times
      with different modes. Fixed by checking if a new statement
      is compatible in the start_stmt function. It nows do the
      same checks than external_lock.
      modified:   storage/connect/ha_connect.cc
      modified:   storage/connect/ha_connect.h

    - typo
      modified:   storage/connect/user_connect.cc

    - Fix GetTableName that returned wrong value under Windows
      modified:   storage/connect/ha_connect.cc

    - Fix MDEV-13136: enhance CREATE SERVER MyServerName
      FOREIGN DATA WRAPPER to work with CONNECT engine
      modified:   storage/connect/tabjdbc.cpp

    - Add a function to retrieve User variable value (DEVELOPMENT only)
      modified:   storage/connect/ha_connect.cc
      modified:   storage/connect/jsonudf.cpp
      modified:   storage/connect/jsonudf.h
      modified:   storage/connect/tabjdbc.cpp

    - Fix MDEV-18192: CONNECT Engine JDBC not able to issue
      simple UPDATE statement from trigger or stored procedure
      modified:   storage/connect/tabext.cpp
      modified:   storage/connect/tabext.h
      modified:   storage/connect/tabjdbc.cpp

    - Enable CONNECT tables to have triggers
      Update version number
      modified:   storage/connect/ha_connect.cc

    - Make user and password defined in CREATE TABLE have precedence on
      the ones specified in a Federated Server.
      modified:   storage/connect/tabjdbc.cpp

    - JSONColumns: Copy locally constant strings to fix error in OEM modules
      modified:   storage/connect/tabjson.cpp

commit 99de7f4e486
Author: Olivier Bertrand <bertrandop@gmail.com>
Date:   Sun Jan 27 15:16:15 2019 +0100

    - Fix MDEV-18192: CONNECT Engine JDBC not able to issue
      simple UPDATE statement from trigger or stored procedure
      modified:   storage/connect/tabext.cpp
      modified:   storage/connect/tabext.h
      modified:   storage/connect/tabjdbc.cpp

    - Enable CONNECT tables to have triggers
      Update version number
      modified:   storage/connect/ha_connect.cc

    - Make user and password defined in CREATE TABLE have precedence on
      the ones specified in a Federated Server.
      modified:   storage/connect/tabjdbc.cpp

    - JSONColumns: Copy locally constant strings to fix error in OEM modules
      modified:   storage/connect/tabjson.cpp

Before killing the server, we must issue FLUSH TABLES in order
to cleanly close any MyISAM system tables, to avoid warnings about
them when restarting.

```----
MySQL abnormally exits on KILL command.

Fix
```

The abnormal exit has been fixed.

RB: 20971, 21129, 21237

For partitioned table, ensure that the AUTO_INCREMENT values will
be assigned from the same sequence. This is based on the following
change in MySQL 5.6.44:

commit aaba359c13d9200747a609730dafafc3b63cd4d6
Author: Rahul Malik <rahul.m.malik@oracle.com>
Date:   Mon Feb 4 13:31:41 2019 +0530

    Bug#28573894 ALTER PARTITIONED TABLE ADD AUTO_INCREMENT DIFF RESULT DEPENDING ON ALGORITHM

    Problem:
    When a partition table is in-place altered to add an auto-increment column,
    then its values are starting over for each partition.

    Analysis:
    In the case of in-place alter, InnoDB is creating a new sequence object
    for each partition. It is default initialized. So auto-increment columns
    start over for each partition.

    Fix:
    Assign old sequence of the partition to the sequence of next partition
    so it won't start over.

    RB#21148
    Reviewed by Bin Su <bin.x.su@oracle.com>

Correctly document the usage of m_max_value. Remove the const
qualifier, so that the implicit assignment operator can be used.
Make all members of ib_sequence private, and add an accessor
member function max_value().

PROBLEM
 =======
An add index doesn't update index length stats in information schema
TABLES table.

FIX
 ===
Update the dict_table_t variable with index length stats that is
actually calculated post alter . As this variable is used to populated
the information schema index length statistics.

Reviewed by: Bin su<bin.x.su@oracle.com>
RB: 21277

Field_bit for BIT(20) uses 2 full bytes in the record,
with additional 4 uneven bits in the "null bit area".

Field::set_default() called from Field_bit::set_default() erroneously
copied 3 bytes instead of 2 bytes from the record with default values.

Changing Field::set_default() to copy pack_length_in_rec() bytes
instead of pack_length() bytes.

In debug builds, this setting is allowed to be turned off temporarily after it was
turned on during startup. Howewer memory garbage also caused it to be accidentally
turned on when it was disabled at startup.