sends down UPDATE statement together with current database name.

Add MTR test for UPDATE.

Multi-UPDATE first sends SELECT to collect constrainsts for the records
to be updated. By default this SELECT uses SH that doesn't suit this.
Add if-block to guard against multi-UPDATE in create_SH().

        Renamed select handler control knob.

        Updated test suite.

      Removed unused code.

    Add a knob to disable Select handler.

        syncronize the schema list at MDB FE and CLX BE.

        Add support for RENAME TABLE.

        Fixed a double free bug in discover_table_details.

texts.

Replaced fixed size uchar arrays for buffers with memory allocations.

Fixed MDB crash in discover_table_details with CX unavailable.

Related to MDEV-21769.

Related to MDEV-21769.

After the '.so' one is supposed to use the directory name, like we have
correctly in all old man pages:
  mysql_client_test_embedded.1:.so man1/mysql_client_test.1
  mysql_embedded.1:.so man1/mysql.1
  mysqltest_embedded.1:.so man1/mysqltest.1

This change adds the 'man1/' component so the link has the correct format.
Actually using man links is a deprecated practice and using symlinks
would be better, but that can be fixed in a later commit.

From https://www.debian.org/doc/debian-policy/ch-docs.html#manual-pages:
> If one man page needs to be accessible via several names it is better
> to use a symbolic link than the .so feature

Detected via Lintian errors:
  E: mariadb-server-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-show.1.gz
  E: mariadb-client-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-binlog.1.gz
  E: mariadb-client-10.5: bad-so-link-within-manual-page usr/share/man/man1/mariadb-plugin.1.gz

Related to MDEV-21769.

This fixes errors like:

  $ LC_ALL=en_US.UTF-8 MANROFFSEQ='' MANWIDTH=80 \
    man --warnings -E UTF-8 -l -Tutf8 -Z mysql-test-run.pl.1 > /dev/null

  troff: <standard input>:246: warning [p 2, 6.0i, div '3tbd1,1', 0.3i]: can't break line
  troff: <standard input>:275: warning [p 2, 6.0i, div '3tbd6,1', 0.8i]: can't break line

Related to MDEV-21769.

Related to MDEV-21769.

Added CYCLE ... RESTRICT (nonstandard) clause to recursive CTE.