Cleanups, fixed warnings from valgrind, fixed failing tests (because on changes in WSREP initialization)

This should not have caused any notable errors in most cases.

After fix, we are not using keys to solve MIN/MAX if the string used for comparision is longer thant the column-

Conflicts:
	sql/item_subselect.cc

Fixed also typo in comment

- Cache variables.lc_messages->errmsgs->errmsgs in variables.errmsgs

This gives us 15 byte less code space and 2 memory references for any access to language dependent message,
of which there are 500 in the server..

In some cases NO_ZERO_DATE did not allow datetime values with zero date part
and non-zero time part (e.g. '0000-00-00 10:20:30.123456').
Allowing values of this kind in all known pieces of the code.

Additional changes :
* On startup, do not initialize wsrep if wsrep_on=0.
* On shutdown, stop wsrep replication only if > 0 wsrep
threads are running.

- Renaming variables so that they don't shadow others (After this patch one can compile with -Wshadow and get much fewer warnings)
- Changed ER(ER_...) to ER_THD(thd, ER_...) when thd was known or if there was many calls to current_thd in the same function.
- Changed ER(ER_..) to ER_THD_OR_DEFAULT(current_thd, ER...) in some places where current_thd is not necessary defined.
- Removing calls to current_thd when we have access to thd

Part of this is optimization (not calling current_thd when not needed),
but part is bug fixing for error condition when current_thd is not defined
(For example on startup and end of mysqld)

Notable renames done as otherwise a lot of functions would have to be changed:
- In JOIN structure renamed:
   examined_rows -> join_examined_rows
   record_count -> join_record_count
- In Field, renamed new_field() to make_new_field()

Other things:
- Added DBUG_ASSERT(thd == tmp_thd) in Item_singlerow_subselect() just to be safe.
- Removed old 'tab' prefix in JOIN_TAB::save_explain_data() and use members directly
- Added 'thd' as argument to a few functions to avoid calling current_thd.

Fixing non-BMP characters to have the same weight, as it was before
MDEV-8418 and MDEV-8417.

MDEV-8418 utf16: compare broken bytes as "greater than any non-broken character"

Fixed several optimizer issues relatied to GROUP BY:

a) Refering to a SELECT column in HAVING sometimes calculated it twice, which caused problems with non determinstic functions

b) Removing duplicate fields and constants from GROUP BY was done too late for "using index for group by" optimization to work

c) EXPLAIN SELECT ... GROUP BY did wrongly show 'Using filesort' in some cases involving "Using index for group-by"


a) was fixed by:
- Changed last argument to Item::split_sum_func2() from bool to int to allow more flags
- Added flag argument to Item::split_sum_func() to allow on to specify if the item was in the SELECT part
- Mark all split_sum_func() calls from SELECT with SPLIT_SUM_SELECT
- Changed split_sum_func2() to do nothing if called with an argument that is not a sum function and doesn't include sum functions, if we are not an argument to SELECT.

This ensures that in a case like
select a*sum(b) as f1 from t1 where a=1 group by c having f1 <= 10;

That 'a' in the SELECT part is stored as a reference in the temporary table togeher with sum(b) while the 'a' in having isn't (not needed as 'a' is already a reference to a column in the result)

b) was fixed by:
- Added an extra remove_const() pass for GROUP BY arguments before make_join_statistics() in case of one table SELECT.

This allowes get_best_group_min_max() to optimize things better.

c) was fixed by:
- Added test for group by optimization in JOIN::exec_inner for
  select->quick->get_type() == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX

item.cc:
- Simplifed Item::split_sum_func2()
  - Split test to make them faster and easier to read
  - Changed last argument to Item::split_sum_func2() from bool to int to allow more flags
  - Added flag argument to Item::split_sum_func() to allow on to specify if the item was in the SELECT part
  - Changed split_sum_func2() to do nothing if called with an argument that is not a sum function and doesn't include sum functions, if we are not an argument to SELECT.

opt_range.cc:
- Simplified get_best_group_min_max() by calcuating first how many group_by elements.
- Use join->group instead of join->group_list to test if group by, as join->group_list may be NULL if everything was optimized away.

sql_select.cc:
- Added an extra remove_const() pass for GROUP BY arguments before make_join_statistics() in case of one table SELECT.
- Use group instead of group_list to test if group by, as group_list may be NULL if everything was optimized away.
- Moved printing of "Error in remove_const" to remove_const() instead of having it in caller.
- Simplified some if tests by re-ordering code.
- update_depend_map_for_order() and remove_const() fixed to handle the case where make_join_statistics() has not yet been called (join->join_tab is 0 in this case)

function used incorrect type.

Fixes over the original patch:
- Fix variable/class/other names
- Fix the JSON output to be in line with the output of other JSON
  constructs we produce

Used wrong type for encryption_key_id and page_compression_level in
table options. Make explicit casts for calls also.

mysqld--help was not updated for binlog row image.

Logic error, NULL pointer was referenced.

File block size might be 0 and used on modulo operator. Make sure that
file block size is initialized to 512.

When writing rows with a minimal row image, it is possible to receive
empty events. In that case m_curr_row and m_rows_end are the same,
however the event implies an insert into the table with the default
values associated for that table.