Markdown README for a prettier github representation

- Sometimes privilege_table_io printed double rows of roles_mapping
  - Fixed by forcing restart of server when running test
- Wsrep_cluster_address_basic failed in some combinations because
  wsrep_cluster_address was set to NULL
  - Fixed by ensuring it's never set to NULL, only empty string

This makes it easier to setup master as on only have to set --log-bin.
Before this patch if one did set up the master with just --log-bin, slaves
could not connect until server_id was set on the master, which could be
both confusing and hard to do.

- When waiting for events, start time is now counted from start of wait
- Instead of having "Connect" as "Command" for all replication threads we
  now have:
  - Slave_IO for Slave thread reading relay log
  - Slave_SQL for slave executing SQL commands or distribution queries to
    Slave workers
  - Slave_worker for slave threads executin SQL commands in parallel replication

use the new approach with Field->default_value expressions.
But keep the old TIMESTAMP_UN_FIELD for ON UPDATE NOW().

to be calculated at the CREATE TABLE time and stored in
the default row image.

expression defaults and check constraints should behave as
constant default values - copied from fields, not copied from expressions

and use the same error message for CREATE and open table time

That is, when the precision of DEFAULT NOW() is less than
the precision of the column, do not convert it to unireg_check,
use the new approach where DEFAULT is tryly an expression.

* revert part of the db7edfed that moved calculations from
  fix_fields to val_str for Item_func_sysconst and descendants
* mark session state dependent functions in check_vcol_func_processor()
* re-run fix_fields for all such functions for every statement
* fix CURRENT_USER/CURRENT_ROLE not to use Name_resolution_context
  (that is allocated on the stack in unpack_vcol_info_from_frm())

Note that NOW(), CURDATE(), etc use lazy initialization and do *not*
force fix_fields to be re-run. The rule is:
* lazy initialization is *not* allowed, if it changes metadata (so,
   e.g. DAYNAME() cannot use it)
* lazy initialization is *preferrable* if it has side effects (e.g.
  NOW() sets thd->time_zone_used=1, so it's better to do it when
  the value of NOW is actually needed, not when NOW is simply prepared)

into "fix" and "check" parts

in a case of a specially crafted invalid frm

as in

create table t1 (a int);
create view v1 as select default(a) as NOT_UPDATABLE from t1;

Call profiling.restart() and profiling.reset() only if profiling is e…

in other case we will get:

../alex/dev/server/sql/sql_class.cc: In member function ‘void THD::free_connection()’:
../server/sql/sql_class.cc:1664:3: error: ‘profiling’ was not declared in this scope
   profiling.restart();                          // Reset profiling
      ^~~~~~~~~

../server/sql/sql_class.cc: In member function ‘void THD::reset_for_reuse()’:
../server/sql/sql_class.cc:1689:3: error: ‘profiling’ was not declared in this scope
  profiling.reset();
       ^~~~~~~~~

errors.

This reverts commit 7b89b9f5.

Based on contributions by Daniel Black and Otto Kekäläinen.

.. logged under row binlog format

In the early stages of ALTER TABLE execution, the implementation
checks whether its a NOOP (alter_info->flags == 0), and if so,
it returns after logging the command to binary log. The logging,
however, was done unconditionally.

Fixed by skipping the logging for temporary tables when under row
based replication.

.. share->last_version' failed in myisam/mi_open.c:67: test_if_reopen

During the RENAME operation since the renamed temporary table is also
opened and added to myisam_open_list/maria_open_list, resetting the
last_version at the end of operation (HA_EXTRA_PREPARE_FOR_RENAME)
will cause an assertion failure when a subsequent query tries to open
an additional temporary table instance and thus attempts to reuse it
from the open table list.

This commit fixes the issue by skipping flush/close operations executed
toward the end of ALTER for temporary tables. It also enables a shortcut
for simple ALTERs (like rename, disable/enable keys) on temporary
tables.

As safety checks, added some assertions at code points that should not
be hit for temporary tables.

Signed-off-by: Daniel Black <daniel.black@au.ibm.com>

This is never hit in practice, because the wrapper code catches it,
but fix the zero length exit to restore all the non volatile registers.

From: https://github.com/antonblanchard/crc32-vpmsum/commit/aaf0ac48a401abfaa0ad2d520be755e66c1e2e95Signed-off-by: Anton Blanchard <anton@samba.org>

These are different from the existing crc32 functions which
where really crc32c.

Move crc32-vpmsum to extra.
Compile static crc32-vpmsum instead of adding sources directly.
Make use of crc32-vpmsum via my_checksum().

Based on contribution by Daniel Black.

Table before collecting engine independent statistics now is reopened in read mode,
InnoDB allow write operations in this case.

The memory alloc-ed initially for wsrep_sst_auth to store the
value specified in config was lost as the global variable was
reset while in process of masking it and thus, could never be
reclaimed on shutdown.