There is a race between two threads: user thread and the dump
thread. The former sets a debug instruction that makes the latter wait
before processing an Xid event. There can be cases that the dump
thread has not yet processed the previous Xid event, causing it to
wait one Xid event too soon, thus causing sync_slave_with_master never
to resume.
      
We fix this by moving the instructions that set the debug variable
after calling sync_slave_with_master.