As discussed on the call:
- s/Window_funcs_computation_step/Window_funcs_computation/g
- s/Window_func_sort/Window_funcs_sort/g

- Rename Window_funcs_computation to Window_funcs_computation_step
- Introduce Window_func_sort which invokes filesort and then
  invokes computation of all window functions that use this ordering.
- Expose Window functions' sort operations in EXPLAIN|ANALYZE FORMAT=JSON

of compare_window_funcs_by_window_specs().

The current implementation does not allow for a dynamic expression
within the sum function's parameter.

The problem popped up when running win_percent_cume.test
with --ps-protocol.

Window names has to be resolved only once.

that the call-back comparison function returns a positive
number when arg1 < arg2, and a negative number when arg1 > arg2.
This is not in line with other implementation of sorting
algorithm.
Changed bubble_sort: now a negative result from the comparison
function means that arg1 < arg2, and positive result means
that arg1 > arg2.
Changed accordingly all call-back functions that are used as
parameters in the call of bubble_sort.

Added a test case to check the proper sorting of window functions.

The function did not take into account the case when only one of
of the pointers to the compared frames is NULL.

This will be useful for window functions development.

of the temporary table needed to compute them.

Also fixed a bug in row_counts detection, when partition changes.

The percent_rank function now is compatible with the cursor algorithm.
We no longer need a special implementation for it to work.

Instead of relying solely on top bound and bottom bound cursors,
now we create a list of cursors that are iterated over.

- Hook window function computation into the right location.
- Add a testcase which shows that HAVING is now checked before
  the window function computation step.

- Make EXPLAIN code use the post-join operations
- Remove Sort_and_group_tracker that was used for that purpose

man page updates: mysqlbinlog options, mysqlcheck clarification and 10.2 updates

We can call setup_partition_border_check() from
JOIN::make_aggr_tables_info(), provided that call is made after
appropriate set_items_ref_array() call.

gbh != NULL is handled in a separate branch above,
we don't get into this part of code when gbh!=NULL

Added class Window_funcs_computation, with setup() method to setup
execution, and exec() to run window function computation.

setup() is currently trivial. In the future, it is expected to optimize
the number of sorting operations and passes that are done over the temp.
table.

as it can return negative values.
The typo was introduced in the patch for MDEV-9665 in 10.2.0.

as they are not used any more.
We now use function templates from strcoll.ic instead.

Fixed calculating pointer to memory allocated for names in numeric format in unpacking procedure.