MDEV-3902  Assertion `record_length == m_record_length' failed at Filesort_buffer::alloc_sort_buffer

This bug is a duplicate of mdev-3899 so adding a test case only.

  
The patch decreases the duration of LOCK_thread_count, so it is not hold during THD destructor and freeing memory.
This mutex  now only protects the integrity of threads list, when removing THD from it,  and thread_count variable.
  
The add_to_status() function that updates global status during client disconnect,  is now correctly protected by the LOCK_status mutex.

Benchmark : in a  "non-persistent" sysbench test (oltp_ro with reconnect after each query),  ~ 25% more connects/disconnects were measured

MDEV-3899  Valgrind warnings (blocks are definitely lost) in filesort on IN subquery with SUM and DISTINCT
  
Analysys:
In the beginning of JOIN::cleanup there is code that is supposed to
free all filesort buffers. The code assumes that the table being sorted
is the first non-constant table. To get this table it calls:
first_top_level_tab(this, WITHOUT_CONST_TABLES)
  
However, first_top_level_tab() instead returned the wrong table - the first
one in the plan, instead of the first non-constant table. There is no other
place outside filesort() where sort buffers may be freed. As a result, the
sort buffer was not freed, and there was a memory leak.
  
Solution:
Change first_top_level_tab(), to test for WITH_CONST_TABLES instead of
WITHOUT_CONST_TABLES.

client/mysqldump.c:
  Removed compiler warning
extra/yassl/taocrypt/include/pwdbased.hpp:
  Removed compiler warning (iterations is always unsigned)
support-files/compiler_warnings.supp:
  Ignore warnings from groff

Fixed the test to be lower-case because it fails on windows with mixed case.

mysql-test/r/create.result:
  Updated test results
mysql-test/t/create.test:
  Updated test
sql/sql_base.cc:
  Use push_internal_handler/pop_internal_handler to avoid errors & warnings instead of clear_error
  Give a warnings instead of an error for CREATE TABLE IF EXISTS
sql/sql_parse.cc:
  Check if we failed because of table exists (can only happen from create)
sql/sql_table.cc:
  Check if we failed because of table exists (can only happen from create)

Analysis:
The reason for the suboptimal plan when querying IS tables through a view
was that the view columns that participate in an equality are wrapped by
an Item_direct_view_ref and were not recognized as being direct column
references.

Solution:
Use the original Item_field objects via the real_item() method.

mysql-test/r/create.result:
  Added test case to show that CREATE TABLE also is not waiting if table exists.
mysql-test/t/create.test:
  Added test case to show that CREATE TABLE also is not waiting if table exists.
sql/sql_base.cc:
  Clear also warnings from acquire_locks if we retry.

- Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
- Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.

mysql-test/r/create.result:
  New test case
mysql-test/t/create.test:
  New test case
sql/sql_base.cc:
  Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
  Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.
sql/sql_base.h:
  Updated prototype
sql/sql_db.cc:
  Added extra argument to call to check_if_table_exists()

Fix of MDEV-3874: Server crashes in Item_field::print on a SELECT from a MERGE view with materialization+semijoin, subquery, ORDER BY.

The problem was that in debugging binaries it try to print item to assign human readable name to the item.
But subquery item was already freed (join_free/cleanup with full cleanup) so Item_field refers to temporary
table which memory had been already freed.

When inserting a record with update on duplicate keys the server calls
the ha_index_read_idx_map handler function to look for the record
that violates unique key constraints. The third parameter of this call
should mark only the base components of the index where the server is
searched for the record. Possible hidden components of the primary key
are to be unmarked.

Fixed typo (missing comma)

If connection kills itself (or own query), it will get an error consistently,
with both COM_PROCESSKILL and with "KILL [QUERY] id"

Assertion happened because sql_kill did not set OK status in diagnostic area
in the case of connection suicide (id to kill == thd->thread_id), issued 
via  COM_PROCESS_KILL , e.g using mysql_kill()

This patch ensures that diagnostic area is initialized in this specific case.

MDEV-736 LP:1004615 - Unexpected warnings "Encountered illegal value '' when converting to DECIMAL" on a query with aggregate functions and GROUP BY

fix: don't call field->val_decimal() if the field->is_null()
because the buffer at field->ptr might not hold a valid decimal value

sql/item_sum.cc:
  do not call field->val_decimal() if the field->is_null()
storage/maria/ma_blockrec.c:
  cleanup
storage/maria/ma_rrnd.c:
  cleanup
strings/decimal.c:
  typo

Fix some problems in the TC_LOG_MMAP commit processing, which could
lead to assertions in some cases.

Problems are mostly reproducible in MariaDB 10.0 with asynchroneous
commit checkpoints, but most of the problems were present in earlier
versions also.

Adjust unstable test case.

Properly drop all unused keys.
Patch by Igor Babaev.

mysql_config:
- add not only $pkgincludedir, but also $pkgincludedir/.. to the header search path,
  for #include <mysql/plugin.h> to work


scripts/mysql_config.sh:
  - don't support headers in */include anymore. only in */include/mysql
  - remove the incorrect "bug fix" (fixed correctly long time ago)
  - add not only $pkgincludedir, but also $pkgincludedir/.. to the header search path,
    for #include <mysql/plugin.h> to work
  - but don't do it, if $pkgincludedir/.. is /usr/include

followup fixes for MySQL Bug #13889741: HANDLE_FATAL_SIGNAL IN _DB_ENTER_ | HANDLE_FATAL_SIGNAL IN STRNLEN

Take into account that length of strings passed down to this function can be up to FN_REFLEN+1 bytes. including terminating zero.
The overwrite was caused by incomplete fix to MySQL Bug # 44834

If triggers are used for an insert/update/delete statement than the values of
all virtual columns must be computed as any of them may be used by the triggers.

add a test case for MySQL Bug #13889741: HANDLE_FATAL_SIGNAL IN _DB_ENTER_ | HANDLE_FATAL_SIGNAL IN STRNLEN