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