post-fix patch for MDEV-5850: MySQL Bug#21317: SHOW CREATE DATABASE does not obey to lower_case_table_names

- Show a line with "Engine-independent statistics collected" when ANALYZE command
  caused EITS statistics to be recollected.

- Dont substract unsigned numbers, use correct calculations.
- (there is no testcase because effort is required to come up with it)

- Move [some] engine-agnostic tests from t/selectivity.test to t/selectivity_no_engine.test
- Move Histogram::point_selectivity to sql_statistics.cc

- Histogram::find_bucket() should not walk off the end of the value range.
- Address review feedback in Histogram::point_selectivity(): different handling
  for zero-width buckets, and explanations.

remove dead code

MDEV-5839 TokuDB tables not properly cleaned on DROP DATABASE

TokuDB does not support discover_table_names() and writes no files
in the database directory, so automatic filename-based
discover_table_names() doesn't work either. So, it must force .frm
file to disk in ::create()

Don't abort plugin reads whem mpvio->make_it_fail is set - this can leak information.

Rename back my_init_dynamic_array2() -> init_dynamic_array2()
It happens to be a part of the de facto API :(

MDEV-5955 Server crashes in handler::ha_external_lock or assertion `m_lock_type == 2' fails in handler::ha_close on disconnect with a locked temporary table

first unlock locked tables, then close and remove temporary

The reason was that a couple of variables that hold number of rows that was used to calculate buffers was uint and caused an overflow.

Fixed by changing variables that could hold number of rows from uint to ulong and also added a cast for this test.

include/heap.h:
  Reorder to get better alignment. Changed variables that could hold number of rows from uint to ulong
mysql-test/suite/heap/heap.result:
  Added test case
mysql-test/suite/heap/heap.test:
  Added test case
mysql-test/suite/plugins/t/server_audit.test:
  Added sleep as we want to have disconnect logged before we try a new connect
storage/heap/ha_heap.cc:
  Changed variables that could hold number of rows from uint to ulong
  Limit number of rows to 4G  (as most of the variables that holds rows are ulong anyway)
  reset records_changed when key_stat_version is changed to not cause increments for every row changed
storage/heap/ha_heap.h:
  changed records_changed to ulong as this can get big
storage/heap/hp_create.c:
  Changed variables that could hold number of rows from uint to ulong
  Added cast (fixed the original bug)
storage/heap/hp_delete.c:
  Changed variables that could hold number of rows from uint to ulong
storage/heap/hp_open.c:
  Removed not needed cast
storage/heap/hp_write.c:
  Changed variables that could hold number of rows from uint to ulong
support-files/compiler_warnings.supp:
  Removed extra : from supression

- Fix Histogram::point_selectivity() to work in the case where the 
  passed value_pos=0 (or 1) and the first (or the last) bucket in the 
  histogram has zero value-range (i.e one value).

[Attempt #2]
- Use a new selectivity calculation formula in Histogram::point_selectivity. 
  The formula is different from the old one because it was developed from scratch.
  it doesn't have any possible division-by-zero problems.

MDEV-5920 MySQL Bug#16765410 FTS: STACK AROUND THE VARIABLE 'MYSTR' WAS CORRUPTED IN INNOBASE_STRNXFRM

MDEV-5861 MySQL Bug#12601974 - STORED PROCEDURE SQL_MODE=NO_BACKSLASH_ESCAPES IGNORED AND BREAKS REPLICATION

escape usernames in CREATE/DROP USER error messages according to NO_BACKSLASH_ESCAPES

simplify the prototype and move it to sql_string.h

  use LEX_STRING, keep similar functions together, remove duplicated code

field list, it doesn't work if ALTER TABLE has replaced all fields.
Instead, pass the correct original table name down from the caller.

from the variable @@session.tokudb_row_format

MDEV-5815 MySQL BUG#11751736: DROP DATABASE STATEMENT SHOULD REMOVE .OLD SUFFIX FROM DATABASE DIRECTORY

Delete .OLD and .TMD files when a MyISAM table is dropped.
Same for Aria.

sql/sql_db.cc:
  dead code - *.TMD cannot be deleted from here.

previous file->index_next (or other file->... index access method)
succeeded

in the libmysqlclient_16 version node.

add pthread_mutex_destroy(&THR_LOCK_dbug); that was apparently
forgotten since the very first MySQL version

error message (because error messages use replacements)

for new tables