branches/zip: Address Issue #350 in comments.

lock_rec_queue_validate(), lock_rec_queue_validate(): Note that
this debug code may violate the latching order and cause deadlocks.

lock/lock0lock.c

@@ -4633,6 +4633,10 @@ lock_rec_queue_validate(
 		next function call: we have to release lock table mutex
 		to obey the latching order */
 
+		/* If this thread is holding the file space latch
+		(fil_space_t::latch), the following check WILL break
+		latching order and may cause a deadlock of threads. */
+
 		impl_trx = lock_sec_rec_some_has_impl_off_kernel(
 			rec, index, offsets);
 
@@ -4756,6 +4760,11 @@ loop:
 
 			lock_mutex_exit_kernel();
 
+			/* If this thread is holding the file space
+			latch (fil_space_t::latch), the following
+			check WILL break the latching order and may
+			cause a deadlock of threads. */
+
 			lock_rec_queue_validate(block, rec, index, offsets);
 
 			lock_mutex_enter_kernel();