Backport the fix to 5.5, because it fails there too

The patch fixes two test failures:
- on slow builders, sometimes a connection attempt which should
  fail due to the exceeded number of thread_pool_max_threads
  actually succeeds;
- on even slow builders, MTR sometimes cannot establish the
  initial connection, and check-testcase fails prior to the
  test start

The problem with check-testcase was caused by connect-timeout=2
which was set for all clients in the test config file. On slow
builders it might be not enough.
There is no way to override it for the pre-test check, so it needed
to be substantially increased or removed.

The other problem was caused by a race condition between sleeps
that the test performs in existing connections and the connect
timeout for the connection attempt which was expected to fail.
If sleeps finished before the connect-timeout was exceeded, it
would allow the connection to succeed.

To solve each problem without making the other one worse,
connect-timeout should be configured dynamically during the test.
Due to the nature of the test (all connections must be busy
at the moment when we need to change the timeout, and cannot execute
SET GLOBAL ...), it needs to be done independently from the server.

The solution:
- recognize 'connect_timeout' as a connection option in mysqltest's
  "connect" command;
- remove connect-timeout from the test configuration file;
- use the new connect_timeout option for those connections which
  are expected to fail;
- re-arrange the test flow to allow running a huge SLEEP
  without affecting the test execution time (because it would be
  interrupted after the main test flow is finished).

The test is still subject to false negatives, e.g. if the connection
fails due to timeout rather than due to the exceeded number of
allowed threads, or if the connection on extra port succeeds due
to a race condition and not because the special logic for the extra
port. But those false negatives have always been possible there
on slow builders, they should not be critical because faster builders
should catch such failures if they appear.

Conflicts:
	client/mysqltest.cc
	mysql-test/r/pool_of_threads.result
	mysql-test/t/pool_of_threads.test

main.log_slow might leave mysql.slow_log table non-empty,
and tests which later use it might fail. Make sure that the table
is properly truncated

and use is_supported_parser_charset() instead of direct check

In file sql/filesort.cc,when merge_buffers() is called then
- queue_remove(&queue,0) is called
- For the function queue_remove there is assertion states that the element to be removed should have index >=1
- this is causing the assertion to fail.

Fixed by removing the top element.

MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)

The patch b96c196f added a new call for
safe_charset_converter() without a corresponding fix_fields().
In case of a sub-query the created Item remained in non-fixed state.
The problem did not show up with literal derived expressions, only
subselects were affected. This patch adds a corresponding fix_fields()
to the previously added safe_charset_converter().

Added test case.

Do not use 0x%p to output thd address, use %p

count duplicate of UNION SELECT separately to awoid influence on lokal LIMIT clause.

Fix st_select_lex::is_merged_child_of to work across merged views or
derived tables.

The bug occurred when a subquery
- has a reference to outside, to grand-parent query or further up
- is converted to a semi-join (i.e. merged into its parent).

Then the reference to outside had form Item_ref(Item_field(...)).
- Conversion to semi-join would call item->fix_after_pullout() for the
  outside reference.
- Item_ref::fix_after_pullout would call Item_field->fix_after_pullout
- The Item_field would construct a new Name_resolution_context object
  This process ignored the fact that the Item_field does not belong to
  any of the subselects being flattened.
The result was crash in the next call to Item_field::fix_fields(), where
we would try to use an invalid Name_resolution_context object.

Fixed by not creating Name_resolution_context object if the Item_field's
context does not belong to the subselect(s) that were flattened.

MDEV-10274 Bundling insert with create statement for table with unsigned Decimal primary key issues warning 1194.

        Flags are important for key_length calculations, so them should
        be set before it, not after.

This change is a backport from 10.0 to 5.5 for:
1. The full patch for:
     MDEV-4841 Wrong character set of ADDTIME() and DATE_ADD()
     9adb6e99

2. A small fragment of:
     MDEV-5298 Illegal mix of collations on timestamp
     03f6778d
   which overrides Item_temporal_hybrid_func::cmp_type(),
   and adds a new line into cache_temporal_4265.result.

double the timeout for threads to die on shutdown

some trivial simplifications. drinking the ocean,
one drop at a time

MDEV-11552 Queries executed by event scheduler are written to slow log incorrectly or not written at all

because thd->update_server_status() is used to measure the query time
for the slow log (not only to set protocol level flags),
it needs to be called also when the server isn't going to send
anything to the client.

        MySQL has a bug failing to handle
           MYSQL_THDVAR_STR(...  PLUGIN_VAR_NOSYSVAR |
                                 PLUGIN_VAR_NOCMDOPT | PLUGIN_VAR_MEMALLOC)
        so fall back to just PLUGIN_VAR_READONLY | PLUGIN_VAR_MEMALLOC
        whem MySQL started.

MDEV-10713: signal 11 error on multi-table update - crash in handler::increment_statistics or in make_select or assertion failure pfs_thread == ((PFS_thread*) pthread_getspecific((THR_PFS)))

Different fix. Don't allow Item_func_sp to be evaluated unless
all tables are prelocked.

Extend the test case to make sure Item_func_sp::val_str is called
(the table must have at least one row for that).

Revert "MDEV-10713: signal 11 error on multi-table update - crash in handler::increment_statistics or in make_select or assertion failure pfs_thread == ((PFS_thread*) pthread_getspecific((THR_PFS)))"

This reverts commit 035a5ac6.

Two minor problems and one regression:
1. caching the value in str_result. Other Item methods may use it,
   destroying the cache. See, for example, Item::save_in_field, where
   str_result is moved to use a local buffer (this failed main.grant)
2. Item_func_conv_charset::safe is now set too late, it's initialized
   only in val_str() but checked before that, this failed many tests
   in optimized builds.

to fix 1 - use tmp_result instead of str_result, to fix 2, use
the else branch in the Item_func_conv_charset constructor to set
safe purely from charset properties.

But this introduces a regression, constant strings can no longer be
converted, say, from utf8 to latin1 (because 'safe' will be false).
This fails few tests too. There is no way to fix it without reverting
the commit and converting constants, as before, in the constructor.

truncate unused IO_CACHE backing store files in binlog_cache_data
to release the disk space they were occupying

        Rpl_filter::parse_filter_rule() made NULL-safe.

check for VIEW/DERIVED fields

MDEV-10713: signal 11 error on multi-table update - crash in handler::increment_statistics or in make_select or assertion failure pfs_thread == ((PFS_thread*) pthread_getspecific((THR_PFS)))

Move expression execution out of Item constructor.

Exclude untouched in prepare phese subqueries from the select/unit tree
because they became unreachable by execution.

The problem was that null_value was not set to "false" on a well-formed row.
If an ill-formed row was followed by a well-forned row, null_value remained
"true" in the call of Item::send() for the well-formed row.

Check for readline before checking for curses headers, because
MYSQL_CHECK_READLINE fails when curses is not found, but
CHECK_INCLUDE_FILES simply remembers the fact and continues.  So if
there's no curses, MYSQL_CHECK_READLINE will abort, the user will then
installs curses and continue the build. Thus, CHECK_INCLUDE_HEADERS
will remember that there is no curses, but other checks from
MYSQL_CHECK_READLINE will remember that curses are there. It will
result in inconsistent HAVE_xxx defines.

Don't assume that a word of n bytes can match a word of
at most n * charset->mbmaxlen bytes, always go for the worst.

MDEV-11171 Assertion `m_cpp_buf <= ptr && ptr <= m_cpp_buf + m_buf_length' failed in Lex_input_stream::body_utf8_append(const char*, const char*)

(cherry picked from commit 7a39efab8a59ebdcd562fb788bc004ff338796ea)