This patch changes the main name of 3 byte character set from utf8 to
utf8mb3. New old_mode UTF8_IS_UTF8MB3 is added and set TRUE by default,
so that utf8 would mean utf8mb3. If not set, utf8 would mean utf8mb4.
use the same restriction for character_set_client on the command line
and from SQL.
Also: remove strange hack from thd_init_client_charset() that contradicted
the manual (collation_connection and character_set_result were not always set)
conflicts:
Text conflict in mysql-test/suite/sys_vars/r/rpl_max_binlog_size_func.result
Text conflict in mysql-test/suite/sys_vars/t/rpl_max_binlog_size_func.test
