DISPLAYED

Added both log_slow_admin_statements and log_slow_slave_statements as server
system variables, that can now be dynamically set at run time and are now
available via SHOW GLOBAL VARIABLES. These behave otherwise in the same way as
the --log-slow-admin-statements and --log-slow-slave-statements server command
options.

There is no need to restart the slave SQL thread for the value of
log_slow_slave_statements to be picked up, as the global variable is re-read
with each successful event applied by the SQL thread.