start_waiting_global_read_lock() should wake up all those who are waiting
for protect_against_global_read_lock to go down to 0: those registered in waiting_for_read_lock
AND those registered in global_read_lock_blocks_commit.


sql/lock.cc:
  start_waiting_global_read_lock() should wake up all those who are waiting
  for protect_against_global_read_lock to go down to 0: those registered in waiting_for_read_lock
  AND those registered in global_read_lock_blocks_commit.