Because NOW() is set to system time, unless overriden.
And both should follow big manual system time changes,
while still coping with lowres system clocks.

Ignoring system time changes is both confusing and
breaks with restarts.

as these fields are always declared NOT NULL anyway

MDEV-15395 Wrong result or Assertion `old_part_id == m_last_part' failed in ha_partition::update_row on slave

Revert commit fd240a10 and add a test case

set m_last_part to something meaningful when opening partitions

just as SHOW CREATE TABLE omits them from the index definition

copy the corresponding line from mysql_prepare_insert()

MDEV-15395 Wrong result or Assertion `old_part_id == m_last_part' failed in ha_partition::update_row on slave

RBR cannot work with system versioning on the master.

row_end column is either system time (not @@timestamp) with microsecond
precision or transaction id. Either way, it'll certainly be different
on the slave. So if the master row contains row_end column, it won't
match on the slave. And if we ignore row_end when comparing,
then some other row might match instead.

and few indentation changes

Remove 1668efb7 that introduced a special magic
behavior for UNIX_TIMESTAMP() in the AS OF context

and delete few garbage-in-garbage-out tests

Vers SQL: force VERS_ALTER_HISTORY_KEEP behavior in the slave thread

MDEV-15191 Assertion `bit < (map)->n_bits' failed in bitmap_is_set
upon INSERT

MDEV-15036 Assertion `!is_set() || (m_status == DA_OK_BULK
&& is_bulk_op())' in Diagnostics_area::set_ok_status or unexpected
ER_RANGE_NOT_INCREASING_ERROR

Vers_parse_info::fix_alter_info(): disallow DROP SYSTEM VERSIONING
for system_time partitioned tables.

add a test case

vers_insert_history_row(): do not insert rows with zero or negative lifetime.

mysql_update(): properly handle error from vers_insert_history_row()

Vers SQL: TRT fix getting TRX_ID by COMMIT_TS

Fixed wrong assumption that records are ordered by COMMIT_TS.
This is anyway a quick hack until tempesta-tech#314 is done.

See also FIXME and TODO in TR_table::query(MYSQL_TIME, bool).

Test: SEES case for trx_id.test [closes #456]

Lots of changes:
* calculate the current history partition in ::external_lock(),
  not in ::write_row() or ::update_row()
* remove dynamically collected per-partition row_end stats
* no full table scan in open_table_from_share to calculate these
  stats, no manual MDL/thr_locks in open_table_from_share
* no shared stats in TABLE_SHARE = no mutexes or condition waits when
  calculating current history partition
* always compare timestamps, don't convert them to MYSQL_TIME
  (avoid DST ambiguity, and it's faster too)
* correct interval handling, 1 month = 1 month, not 30 * 24 * 3600 seconds
* save/restore first partition start time, and count intervals from there
* only allow to drop first partitions if INTERVAL
* when adding new history partitions, split the data in the last history
  parition, if it was overflowed
* show partition boundaries in INFORMATION_SCHEMA.PARTITIONS

partition_info had a bunch of function pointers to avoid if()'s
when invoking part_type specific functionality (like get_part_id, etc).
But check_range_constants() and check_list_constants() were still
invoked conditionally, with if()'s.

Create partition_info::check_constants function pointer, get rid
of if()'s

Also remove alloc argument of check_range_constants(), added
in 26a3ff0a. Broken system versioning will be fixed in
following commits.

use include/have_xxx.inc when some feature needs to be present
(because --xxx in the opt file will fail if the xxx is not compiled in)

set variables in the test, not on the command line, to avoid unnecessary
server restarts (they're must slower than SET).

* TIMESTAMP precedence fixed.

Unit-based history point (vers_history_point_t; Vers_history_point).

Update partition stats on ha_partition::write_row()

SQL: DROP PERIOD FOR SYSTEM_TIME syntax

and remove ER_VERS_SYS_FIELD_EXISTS

originally by: Eugene Kosov

also, don't rotate versioning partitions for DELETE HISTORY

originally by: Aleksey Midenkov

implement log-term TODO item, convert redundant if()-s into asserts.