remove thd->find_temporary_table()

Temporarily disable a test for
commit 2175bfce
because fixing it in 10.2 requires updating libmariadb.

buf_page_is_corrupted(): Read the global variable srv_checksum_algorithm
only once in order to avoid a race condition when
SET GLOBAL innodb_checksum_algorithm=...;
is being executed concurrently with this function.

  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

Store original charset during client authentication, and restore it for
COM_RESET_CONNECTION

This is joint work with Oleksandr Byelkin.

wsrep_certification_rules: Define as a weak global symbol.
While there are separate _embedded.a for statically
linked storage engine plugins, there is only one ha_innodb.so
which is supposed to work with both values of WITH_WSREP.

The merge from 10.0-galera introduced a reference to a global
variable that is only defined when the server is built WITH_WSREP.
We must define that symbol as weak global, so that when
a dynamically linked InnoDB or XtraDB is used with the embedded
server (which never includes write-set replication patches),
the variable will be read as 0, instead of causing a failure to
load the InnoDB or XtraDB plugin.

This patch contains the port of the MDEV-18379 patch
for 10.2 branch, but also includes a number of changes
made within MDEV-17835, which are necessary for the
normal operation of tests that use IPv6:

1) Currently, the three-node mtr suite for Galera (galera_3nodes)
uses a separate IPv6 availability check using the "have_ipv6.inc"
file. This check duplicates a more accurate check at suite.pm
level, which can be used by including the file "check_ipv6.inc".
This patch removes this discrepancy between suites.

2) Fixed numerous bugs in the SST scripts and in the mtr test
files (galera_3nodes mtr suite) that prevented the use of Galera
with IPv6 addresses.

3) Fixed flaws in the galera_3nodes mtr suite control scripts,
because of which they could not work with mariabackup.

4) Fixed flaws in the rsync and mysqldump tests (for galera_3nodes
mtr tests suite). These tests were not performed successfully
without these fixes.

5) GAL-501 test in the galera_3nodes suite does not contain the
option "--bind-address=::" that is needed for the test to work
correctly with IPv6 (at least on some systems), since without
it the server will not wait for connections on the IPv6
interface.

https://jira.mariadb.org/browse/MDEV-18379
and partially https://jira.mariadb.org/browse/MDEV-17835

No need to lowercase table names on case-sensitive file systems, as the
cache won't contain the 'lowercased' table anyway. And it prevents the
UPPERCASE.frm from being deleted.

Only starting with MariaDB 10.2, the .result file will echo
"connect" and "connection" statements. There is no way how
the test could have passed on debug builds after
commit 1037edcb
(which looks like an untested backport from a later version).

Problem:
=======
Mariabackup incremental prepare creates new tablespace when it encounter
new tablespace. It sets the intial size as FIL_IBD_FILE_INITIAL_SIZE (4).
But while applying redo log, it tries to access 5th page and then
it leads to out of tablespace error.

Fix:
===
While parsing the redo log record, track FSP_SIZE in recv_spaces for the
respective space id. Assign the recv_size for the tablespace when it
is loaded. Extend the tablespace depends on recv_size while applying
the redo log record.

- Added retry logic if validation of first page fails with checksum
mismatch.

Do not try to write ER_SHUTDOWN error message to socket, when it is forcefully closed by the shutdown.
This will avoid the race condition (attempt to write to closed socket,  if connection shuts down by itself).

Analysis:
========
Increasing the length of the indexed varchar column is not an instant operation for
innodb.

Fix:
===
- Introduce the new handler flag 'Alter_inplace_info::ALTER_COLUMN_INDEX_LENGTH' to
indicate the index length differs due to change of column length changes.

- InnoDB makes the ALTER_COLUMN_INDEX_LENGTH flag as instant operation.

This is a port of Mysql fix.

    commit 913071c0b16cc03e703308250d795bc381627e37
    Author: Nisha Gopalakrishnan <nisha.gopalakrishnan@oracle.com>
    Date:   Wed May 30 14:54:46 2018 +0530

        BUG#26848813: INDEXED COLUMN CAN'T BE CHANGED FROM VARCHAR(15)
                      TO VARCHAR(40) INSTANTANEOUSLY

ha_innobase::commit_inplace_alter_table(): Do not crash if
innobase_update_foreign_cache() returns an error. It can return
an error on ALTER TABLE if an inconsistent FOREIGN KEY constraint
was created earlier when SET foreign_key_checks=0 was in effect.
Instead, report a warning to the client that constraints cannot
be loaded.

ha_innobase::prepare_inplace_alter_table(): Filter out duplicates
from ha_alter_info->alter_info->drop_list.elements.

innobase_rename_column_try(): Declare fk_evict as std::set
instead of std::list, in order to filter out duplicates.

@@open_files_limit now behaves differenly and cannot
be used to skip the test anymore.

Reverting part of da34c7de that was already fixed by MDEV-17531 by Marko