WL#1432: MySQL Cluster: Transaction consistency

Transaction concistency between threads in same and other MySQL Servers using 
the MySQL Cluster. This is known to be working between different Ndb client 
threads but this has to be checked from MySQL Server level. 

For example:
* should a read of a records that later should be updated take an exclusive 
lock? This is not the case now.
* Isolation levels? I have seen in innodb code that different isolation levels 
are used.

This worklog task is written more or less as a note that someone should check 
that locks are held correctly during a transaction.