fix bug #691234
bool variables in mysql can be used without argument in command-line and config.
Example:
--use_global_long_query_time
Variables what can be used without argument named "optional".
Bug #691234 provocated by "required" type of variable - as result,
--use_global_long_query_time --log_slow_verbosity="full"
interpreted as:
use_global_long_query_time="--log_slow_berbosity=\"full\""
as effect:
use_global_long_query_time=0 and log_slow_verbosity not setuped