Resolved window names.
Checked some constraints for window frames.
Added test cases for window name resolution.

- Add temporary code: clone_read_record() clones READ_RECORD structure,
  as long as it is used for reading filesort() result that fits into
  memory.
- Add frame bounds for ROWS-type frames. ROWS n PRECEDING|FOLLOWING,
  ROWS UNBOUNDED PRECEDING|FOLLOWING, CURRENT ROW are supported.
- Add Item_sum_count::remove() which allows "streaming" computation
  of COUNT() over a moving frame.

- Make queries that use multiple window functions not to leak memory
- Code cleanup in sql_window.cc

These do not have any meaning after MDEV-8646. Their only valid values are
- table_access_tabs= join_tab;
- top_table_access_tabs_count= top_join_tab_count;

Disable the code that attempts to group window functions together
by their PARTITION BY / ORDER BY clauses, because
1. It doesn't work: when I issue a query with just one window function,
  and no indexes on the table, filesort is not invoked at all.
2. It is not possible to check that it works currently.

Add my own code that does invoke filesort() for each window function.
- Hopefully the sort criteria is right
- Debugging shows that filesort operates on {sort_key, rowid} pairs (OK)
- We can read the filesort rowid result in order.

a separate function, JOIN::process_window_functions().

Debug printout should not attempt to print Ref_ptr_array value as %p.

"Distinct" optimization is not used by this query (both in this tree
and in mainline 10.2). Verified this in debugger.

- All parsing problems look like resolved
- Stub performing name resolution of window functions
in simplest queries has been added.

"Re-factor the code for post-join operations".

The patch mainly contains the code ported from mysql-5.6 and
created for two essential architectural changes:
1. WL#5558: Resolve ORDER BY execution method at the optimization stage
2. WL#6071: Inline tmp tables into the nested loops algorithm

The first task was implemented for mysql-5.6 by Ole John Aske.
It allows to make all decisions on ORDER BY operation at the optimization
stage.

The second task implemented for mysql-5.6 by Evgeny Potemkin adds JOIN_TAB
nodes for post-join operations that require temporary tables. It allows
to execute these operations within the nested loops algorithm that used to
be used before this task only for join queries. Besides these task moves
all planning on the execution of these operations from the execution phase
to the optimization phase.

Some other re-factoring changes of mysql-5.6 were pulled in, mainly because
it was easier to pull them in than roll them back. In particular all
changes concerning Ref_ptr_array were incorporated.

The port required some changes in the MariaDB code that concerned the
functionality of EXPLAIN and ANALYZE. This was done mainly by Sergey
Petrunia.

MDEV-9408 CREATE TABLE SELECT MAX(int_column) creates different columns for table vs view

There were three almost identical pieces of the code:
- Field *Item_func::tmp_table_field();
- Field *Item_sum::create_tmp_field();
- Field *create_tmp_field_from_item();
with a difference in very small details (hence the bugs):
Only Item_func::tmp_table_field() was correct, the other two were not.
Removing the two incorrect pieces of the redundant code.
Joining these three functions/methods into a single virtual method
Item::create_tmp_field().
Additionally, moving Item::make_string_field() and
Item::tmp_table_field_from_field_type() from the public into the
protected section of the class declaration, as they are now not
needed outside of Item.

MDEV-9220 Split filesort.cc:make_sortkey() and filesort.cc::sortlength() into virtual methods in Type_handler

Also fixes:
MDEV-9391 InnoDB does not produce warnings when doing WHERE int_column=varchar_column
MDEV-9337 ALTER from DECIMAL and INT to DATETIME returns a wrong result
MDEV-9340 Copying from INT/DOUBLE to ENUM is inconsistent
MDEV-9392 Copying from DECIMAL to YEAR is not consistent about warnings

Fix process  handle leak in buildbot. GenerateConsoleCtrlEvent sent to non-existing process will add a process handle to this non-existing process to console host process conhost.exe

Fixed main.shutdown failure on Windows.

as it's needed for Cassandra in 10.0.

Perform database installation in one mysqld run. This makes mysql_install_db
3x faster.

Provided IBM System Z have outdated compiler version, which supports gcc sync
builtins but not gcc atomic builtins. It also has weak memory model.

InnoDB attempted to verify if __sync_lock_test_and_set() is available by
checking IB_STRONG_MEMORY_MODEL. This macro has nothing to do with availability
of __sync_lock_test_and_set(), the right one is HAVE_ATOMIC_BUILTINS.

Provided IBM System Z have outdated compiler version, which supports gcc sync
builtins but not gcc atomic builtins. It also has weak memory model.

InnoDB attempted to verify if __sync_lock_test_and_set() is available by
checking IB_STRONG_MEMORY_MODEL. This macro has nothing to do with availability
of __sync_lock_test_and_set(), the right one is HAVE_ATOMIC_BUILTINS.