thd_specifics service

when many plugins are active, all must approve the password

don't do it in the parser, one should not make run-time
decisions (like, checking thd->variables.old_passwords variable)
during parsing.

* indeed, "username IDENTIFIED BY PASSWORD hash" is the same
  as "username IDENTIFIED VIA mysql_native_password USING hash"
* LEX_USER::password can now be used for plain-text passwords

REQUIRE and MAX_QUERIES_PER_HOUR can not possibly apply to a role

* remove no-op check_password_policy() and references to it
* add 'static' to functions that need it
* remove unused function check_acl_user()

  username IDENTIFIED BY PASSWORD xxx
  username IDENTIFIED VIA mysql_native_password USING xxx
  etc

also check for valid strlen(xxx)

* test for opt->name being non-NULL *before* dereferencing it
* remove unused argument in cleanup_variables()
* simplify

Rows_log_event::write_row - don't optimize DELETE+INSERT
into UPDATE if RBR triggers are used

revert the patch for "out parameters in prepare"

as CHARSET_INFO is already const, using const on it
is redundant and results in compiler warnings (on Windows)

1. don't cast size_t* to int*
2. remove long obsolete register specifier

fail CREATE SERVER foreign data wrapper is "mysql"
and neither HOST nor SOCKET are specified.

Also default PORT to 3306 (again, only for foreign
data wrapper "mysql")

* pass LEX_STRING's from the parser, don't ignore the length only to strlen later
* init LEX::server_options only for SERVER commands, not for every statement
* don't put temporary values into a global persistent memroot

but really it's just scratching a surface

Implementation for domain ID based filtering of replication events.