Allow passwordless login in addition to usual login with password, when
creating 'root' user during install.

The effect of that change is that "local administrators" group are
allowed to connect as root user. This is done via gssapi authentication
plugin.

Clients that are not aware of gssapi client plugin, can still login with
password credentials.

Make sure that EXPLAIN object allocated on runtime arena.

from mysql-test-run.

it's now redundant

print PUBLIC not quoted in SHOW GRANTS, PUBLIC is not a role

* "public" should work in any letter case
* PUBLIC is not a valid definer
* granting to public should auto-create an entry in mysql.global_priv
* SHOW GRANTS should show privileges obtained via PUBLIC
* LEX_USER::is_public was often uninitialized
* comments, whitespaces, typos, etc

MDEV-5215 prerequisite of prerequisite: if DB is not mentioned in connect ignore errors of switching to it

MDEV-29924 Assertion `(((nr) % (1LL << 24)) % (int) log_10_int[6 - dec]) == 0' failed in my_time_packed_to_binary on SELECT when using TIME field

when assigning the cached item to the Item_cache for the first time
make sure to use Item_cache::setup(), not Item_cache::store().
Because the former copies the metadata (and allocates memory, in case
of Item_cache_row), and Item_cache::decimal must be set for
comparisons to work correctly.

Revert "MDEV-27233 Server hangs when using --init-file which loads Spider and creates a Spider table"

This reverts commit c160a115.

also call top_level_transform() recursively for

(a OR b) AND (c OR d)

it's incorrect to use change_item_tree() to replace arguments
of top-level AND/OR, because they (arguments) are stored in a List,
so a pointer to an argument is in the list_node, and individual
list_node's of top-level AND/OR can be deleted in Item_cond::build_equal_items().
In that case rollback_item_tree_changes() will modify the deleted object.

Luckily, it's not needed to use change_item_tree() for top-level
AND/OR, because the whole top-level item is copied and preserved
in prep_where and prep_on, and restored from there.

So, just don't.

Post-push fix. The flag of transaction which indicates that it's necessary
to forbid gap lock inheritance after XA PREPARE could be inverted if
lock_release_on_prepare_try() is invoked several times. The fix is to
toggle it on lock_release_on_prepare() exit.

Specifically:

Revert "MDEV-29664 Assertion `!n_mysql_tables_in_use' failed in innobase_close_connection"
This reverts commit ba875e93.

Revert "MDEV-29620 Assertion `next_insert_id == 0' failed in handler::ha_external_lock"
This reverts commit aa08a744.

Revert "MDEV-29628 Memory leak after CREATE OR REPLACE with foreign key"
This reverts commit c579d66b.

Revert "MDEV-29609 create_not_windows test fails with different result"
This reverts commit cb583b2f.

Revert "MDEV-29544 SIGSEGV in HA_CREATE_INFO::finalize_locked_tables"
This reverts commit dcd66c38.

Revert "MDEV-28933 CREATE OR REPLACE fails to recreate same constraint name"
This reverts commit cf6c5176.

Revert "MDEV-28933 Moved RENAME_CONSTRAINT_IDS to include/sql_funcs.h"
This reverts commit f1e1c133.

Revert "MDEV-28956 Locking is broken if CREATE OR REPLACE fails under LOCK TABLES"
This reverts commit a228ec80.

Revert "MDEV-25292 gcol.gcol_bugfixes --ps fix"
This reverts commit 24fff826.

Revert "MDEV-25292 Disable atomic replace for slave-generated or-replace"
This reverts commit 2af15914.

Revert "MDEV-25292 backup_log improved"
This reverts commit 34398a20.

Revert "MDEV-25292 Atomic CREATE OR REPLACE TABLE"
This reverts commit 93c8252f.

Revert "MDEV-25292 Table_name class for (db, table_name, alias)"
This reverts commit d145dda9.

Revert "MDEV-25292 ha_table_exists() cleanup and improvement"
This reverts commit 409b8a86.

Revert "MDEV-25292 Cleanups"
This reverts commit 595dad83.

Revert "MDEV-25292 Refactoring: moved select_field_count into Alter_info."
This reverts commit f02af1d2.