   MASTER_POS_WAIT(log_name,log_pos[,timeout])

This function is useful for control of master/slave synchronization.
It blocks until the slave has read and applied all updates up to the specified
position in the master log.
The return value is the number of log events it had to wait for to get to
the specified position.  The function returns NULL if the slave SQL thread
is not started, the slave's master information is not initialized, the
arguments are incorrect, or an error occurs. It returns -1 if the
timeout has been exceeded. If the slave SQL thread stops while
MASTER_POS_WAIT() is waiting, the function returns NULL.
If the slave is past the specified position, the function returns
immediately.
