Backport from mysql 5.7. The patch reviewed, test added.

MDEV-6220 mysqldump will not backup database with --flush-logs parameter and log_error my.cnf parameter defined

some checks were "if [ -n "$err_log" ]", others were "if [ $want_syslog -eq 0 ]",
so when both are set, error log file was only partially initialized.
To avoid this ambiguity we reset want_syslog when error log file is used.

correct the check for PLUGIN_VAR_STR

mtr internally does the following:
1. $default_vardir=....
2. $opt_vardir=$default_vardir unless $opt_vardir;
3. $opt_vardir=realpath $opt_vardir unless IS_WINDOWS
4. if ($opt_vardir eq $default_vardir) { .... use /dev/shm ... }

thus we have to realpath $default_datadir too, otherwise
the comparison logic might be broken

add "mysql-compat-server" alias to MariaDB-server package

it's in the dead code (ifdef-ed out) so it doesn't matter what it is.
still better to keep it closer to the upstream

Let mtr handle SIGHUP the same way as SIGINT. This solves stale mysqld processes
left after broken/closed ssh connection.

            mysql.service failed to load

Added 'systemctl daemon-reload' command in postin and
postun rpm scripts.

mysql_alter_table() that is used in mysql_recreate_table() doesn't expect
many tables in the TABLE_LIST.

adjust enum values when reading them from frm

workaround for missing SP auto-reparse.
allow the user to disable stored_program_cache_size, if he wants

The test case tried to trigger a DEBUG_SYNC point at the end of a SELECT
SLEEP(5) statement. It did this by using EXECUTE 2, intending to trigger first
at the end of SET DEBUG_SYNC, and second at the end of the SELECT SLEEP(5).

However, in --ps-protocol mode, this does not work, because the SELECT is
executed in two steps (Prepare followed by Execute). Thus, the DEBUG_SYNC got
triggered too early, during the Prepare stage rather than Execute, and the
test case could race and information_schema.processlist see the thread in the
wrong state.

This patch fixes by changing the way the DEBUG_SYNC point is triggered. Now we
add a DBUG injection inside the code for SLEEP(5). This ensures that the
DEBUG_SYNC point is not activated until the SLEEP(5) is running, ensuring
that the following wait for completion will be effective.

DB-787 the tokudb_report_fractal_tree_info_for_db function can leak a db on an error path where db->open fails

Patch by James Taylor.

DB-766 use an extra flag that is supported on MySQL and does not require a tokutek patch to the wait_while_table_is_used function

generate_derived_keys_for_table() did not work correctly in the case where
- it had a potential index on derived table
- however, TABLE::check_tmp_key() would disallow creation of this index 
  after looking at its future key parts (because of the key parts exceeding 
  max. index length)
- the code would leave a KEYUSE structure that refers to a non-existant index.
  Depending on further optimizer calculations, this could cause a crash. 

MDEV-7150 Wrong auto increment values on INSERT .. ON DUPLICATE KEY UPDATE when the inserted columns include NULL in an auto-increment column

when restoring auto-inc value in INSERT ... ON DUPLICATE KEY UPDATE, take into account that
1. it may be changed in the UPDATE clause (old code did that)
2. it may be changed in the INSERT clause and then cause a dup key (old code missed that)