Part of MDEV-13073 AliSQL Optimize performance of semisync

Did the following renames to match other similar variables
key_ss_mutex_LOCK_binlog_       > key_LOCK_bing
key_ss_cond_COND_binlog_send_  -> key_COND_binlog_send
COND_binlog_send_              -> COND_binlog_send
LOCK_binlog_                   -> LOCK_binlog

debian/mariadb-server-10.2.install does not install semisync libs.

Implement --semi-sync-master-wait-point=AFTER_SYNC|AFTER_COMMIT.

When AFTER_SYNC, the semi-sync wait will be done earlier, before the storage
engine commit rather than after. This means that a transaction will not be
visible on the master until at least one slave has received it.

Fix the bug properly (plugin cannot be unloaded as long as it's locked).
Enable and fix the test case.
Significantly reduce number of LOCK_plugin locks for semisync
(practically all locks were removed)

and small collateral changes

mysql-test/lib/My/Test.pm:
  somehow with "print" we get truncated writes sometimes
mysql-test/suite/perfschema/r/digest_table_full.result:
  md5 hashes of statement digests differ, because yacc token codes are different in mariadb
mysql-test/suite/perfschema/r/dml_handler.result:
  host table is not ported over yet
mysql-test/suite/perfschema/r/information_schema.result:
  host table is not ported over yet
mysql-test/suite/perfschema/r/nesting.result:
  this differs, because we don't rewrite general log queries, and multi-statement
  packets are logged as a one entry. this result file is identical to what mysql-5.6.5
  produces with the --log-raw option.
mysql-test/suite/perfschema/r/relaylog.result:
  MariaDB modifies the binlog index file directly, while MySQL 5.6 has a feature "crash-safe binlog index" and modifies a special "crash-safe" shadow copy of the index file and then moves it over. That's why this test shows "NONE" index file writes in MySQL and "MANY" in MariaDB.
mysql-test/suite/perfschema/r/server_init.result:
  MariaDB initializes the "manager" resources from the "manager" thread, and starts this thread only when --flush-time is not 0. MySQL 5.6 initializes "manager" resources unconditionally on server startup.
mysql-test/suite/perfschema/r/stage_mdl_global.result:
  this differs, because MariaDB disables query cache when query_cache_size=0. MySQL does not
  do that, and this causes useless mutex locks and waits.
mysql-test/suite/perfschema/r/statement_digest.result:
  md5 hashes of statement digests differ, because yacc token codes are different in mariadb
mysql-test/suite/perfschema/r/statement_digest_consumers.result:
  md5 hashes of statement digests differ, because yacc token codes are different in mariadb
mysql-test/suite/perfschema/r/statement_digest_long_query.result:
  md5 hashes of statement digests differ, because yacc token codes are different in mariadb
mysql-test/suite/rpl/r/rpl_mixed_drop_create_temp_table.result:
  will be updated to match 5.6 when alfranio.correia@oracle.com-20110512172919-c1b5kmum4h52g0ni and anders.song@greatopensource.com-20110105052107-zoab0bsf5a6xxk2y are merged
mysql-test/suite/rpl/r/rpl_non_direct_mixed_mixing_engines.result:
  will be updated to match 5.6 when anders.song@greatopensource.com-20110105052107-zoab0bsf5a6xxk2y is merged

This patch:

- Moves all definitions from the mysql_priv.h file into
  header files for the component where the variable is
  defined
- Creates header files if the component lacks one
- Eliminates all include directives from mysql_priv.h
- Eliminates all circular include cycles
- Rename time.cc to sql_time.cc
- Rename mysql_priv.h to sql_priv.h