- mysql_install_db now prints position to error file, if log-error is used
- Warning about compatibility now mentions MySQL 5.6 and 5.7
- Give warning if --show_compatibility_56 is used

This was done to make thing consistent. It gives the additional benefit
that EXPLAIN EXTENDED now treat null_tables like constant's and replaces
columns with NULL, in a similar way that it replaces columns with constants
for constant tables.

- Null tables are tables where all columns are always NULL. The most common
  NULL TABLE is a table used in a LEFT_JOIN that is never true.
- All result changes comes from replacing columns with NULL for null_tables.
- "Impossible where" is now also shows constants for const columns.
- Removed duplicated s->type= JT_CONST
- Reset found_const_table_map when JOIN is created (safety fix)

srv_purge_wakeup(): If thd_destructor_proxy has initiated the first
step of shutdown, ensure that all purge threads terminate.

logs_empty_and_mark_files_at_shutdown(): Add a debug assertion.
(The purge threads should have been shut down already before this step.)

(possibly intermittent) checksum mismatch.

trx_set_rw_mode() is never called for read-only transactions, this is guarded
by callers.

Removing this condition from critical section immediately gives 5% scalability
improvement in OLTP index updates benchmark.

is detected.

The checksum mismatch can be due to partial write, thus retry the read

From comment in unreg.h:

  Types of values in the MariaDB extra2 frm segment.
  Each value is written as
    type:       1 byte
    length:     1 byte  (1..255) or \0 and 2 bytes.
    binary value of the 'length' bytes.

length == 1 is valid.

Window is a reserved keyword according to SQL Standard 2016. However, we
can make the grammar slightly flexible by allowing WINDOW keyword everywhere
except table aliases. Change yacc grammar to separate between all keywords
and table_alias keywords.

1. Removing data type specific constants from enum_item_param_state,
   adding SHORT_DATA_VALUE instead.
2. Replacing tests for Item_param::state for the removed constants to
   tests for Type_handler::cmp_type() against {INT|REAL|TIME|DECIAML}_RESULT.
   Deriving Item_param::PValue from Type_handler_hybrid_field_type,
   to store the data type handler of the current value of the parameter.

3. Moving Item_param::decimal_value and Item_param::str_value_ptr
   to Item_param::PValue. Adding Item_param::PValue::m_string
   and changing Item_param to use it to store string values,
   instead of Item::str_value. The intent is to replace Item_param::value
   to a st_value based implementation in the future, to avoid duplicate code.
   Adding a sub-class Item::PValue_simple, to implement
   Item_param::PValue::swap() easier.
   Remaming Item_basic_value::fix_charset_and_length_from_str_value()
   to fix_charset_and_length() and adding the "CHARSET_INFO" pointer
   parameter, instead of getting it directly from item->str_value.charset().
   Changing Item_param to pass value.m_string.charset() instead
   of str_value.charset().
   Adding a String argument to the overloaded
   fix_charset_and_length_from_str_value() and changing Item_param
   to pass value.m_string instead of str_value.

4. Replacing the case in Item_param::save_in_field() to a call
   for Type_handler::Item_save_in_field().

5. Adding new methods into Item_param::PValue:
   val_real(), val_int(), val_decimal(), val_str().
   Changing the corresponding Item_param methods
   to use these new Item_param::PValue methods
   internally. Adding a helper method
   Item_param::can_return_value() and removing
   duplicate code in Item_param::val_xxx().

6. Removing value.set_handler() from Item_param::set_conversion()
   and Type_handler_xxx::Item_param_set_from_value().
   It's now done inside Item_param::set_param_func(),
   Item_param::set_value() and Item_param::set_limit_clause_param().

7. Changing Type_handler_int_result::Item_param_set_from_value()
   to set max_length using attr->max_length instead of
   MY_INT64_NUM_DECIMAL_DIGITS, to preserve the data type
   of the assigned expression more precisely.

8. Adding Type_handler_hybrid_field_type::swap(),
   using it in Item_param::PValue::swap().

9. Moving the data-type specific code from
   Item_param::query_val_str(), Item_param::eq(),
   Item_param::clone_item() to
   Item_param::value_query_type_str(),
   Item_param::value_eq(), Item_param::value_clone_item(),
   to split the "state" dependent code and
   the data type dependent code.
   Later we'll split the data type related code further
   and add new methods in Type_handler. This will be done
   after we replace Item_param::PValue to st_value.

10. Adding asserts into set_int(), set_double(), set_decimal(),
   set_time(), set_str(), set_longdata() to make sure that
   the value set to Item_param corresponds to the previously
   set data type handler.

11. Adding tests into t/ps.test and suite/binlog/t/binlog_stm_ps.test,
   to cover Item_param::print() and Item_param::append_for_log()
   for LIMIT clause parameters.
   Note, the patch does not change the behavior covered by the new
   tests. Adding for better code coverage.

12. Adding tests for more precise integer data type in queries like this:
    EXECUTE IMMEDIATE
     'CREATE OR REPLACE TABLE t1 AS SELECT 999999999 AS a,? AS b'
      USING 999999999;
    The explicit integer literal and the same integer literal
    passed as a PS parameter now produce columns of the same data type.
    Re-recording old results in ps.result, gis.result, func_hybrid_type.result
    accordingly.

- get rid of casts between int and HANDLE.
- store file descriptor in TP_connection_generic to get
rid of multiple mysql_socket_getfd(c->thd->net.vio->mysql_socket))

Also support named pipes (no reason not to support, since it is easy)

UT_RELAX_CPU() is supposed to waste a few CPU cycles, there's no need to
load other system components.

Server already has HMT_low/HMT_medium.

gcc_sync.h, solaris.h, generic-msvc.h copied verbatim.

mariabackup fails to builds with PFS disabled. The reason was missing include,
which was included by PFS otherwise.

# Conflicts:
#	storage/innobase/include/os0file.h

When Mariabackup is invoked on an instance that uses a multi-file
InnoDB system tablespace, it may fail to other files of the system
tablespace than the first one.
This was revealed by the MDEV-14447 test case.
The offending code is assuming that the first page of each data file
is page 0. But, in multi-file system tablespaces that is not the case.

xb_fil_cur_open(): Instead of re-reading the first page of the file,
rely on the fil_space_t metadata that already exists in memory.

xb_get_space_flags(): Remove.

mariabackup fails to builds with PFS disabled. The reason was missing include,
which was included by PFS otherwise.

Running mysqld with innodb-buffer-pool-instances > 1 hangs on startup.

On startup wrong variables was being used to detect number of page cleaner
threads. As a result no threads were actually started. And subsequent code
waits for threads to start forever.

Fixed by using page_cleaner->n_workers, which holds number of page cleaner
threads (0 at startup) instead of srv_n_page_cleaners, which holds number
of requested page cleaner threads (4 by default).

- sql_prepare.cc: Moving functions set_param_xxx() as
  methods to Item_param

- Replacing a pointer to a function Item_param::set_param_func
  to Type_handler based implementation:
  Item_param::value now derives from Type_handler_hybrid_field_type.
  Adding new virtual methods Type_handler::Item_param_setup_conversion()
  and Type_handler::Item_param_set_param_func()

- Moving declaration of some Item_param members  from "public:" to "private:"
  (CONVERSION_INFO, value, decimal_value)

- Adding a new method Item_param::set_limit_clause_param(),
  to share duplicate code, as well as to encapsulate
  Item_param::value.

- Adding Item_param::setup_conversion_string() and
  Item_param::setup_conversion_blob() to share
  the code for binding from a client value
  (mysql_stmt_bind_param), and for binding from
  an expression (Item).

- Removing two different functions set_param_str_or_null()
  and set_param_str(). Adding a common method Item_param::set_param_str().
  Item_param::m_empty_string_is_null, used by Item_param::set_param_str().

- Removing the call for setup_one_conversion_function() from
  insert_params_from_actual_params_with_log(). It's not needed,
  because the call for ps_param->save_in_param() makes sure
  to initialized all data type dependent members properly,
  by calling setup_conversion_string() from
  Type_handler_string_result::Item_param_set_from_value()
  and by calling setup_conversion_blob() from
  Type_handler_blob_common::Item_param_set_from_value()

- Cleanup: removing multiplication to MY_CHARSET_BIN_MB_MAXLEN
  in a few places. It's 1 anyway, and will never change.

Update C/C to include fix for this bug.