WL#395: UNLOCK TABLES table1, table2, table3

Currently to perform atomic operation one would need to lock the set of tables 
used in the following operations and then unlock them at once.

Althought there are many cases then you do not have to hold lock against all 
the tables that long time, and so this may be done by unlocking some of the 
tables.

This is safe as it can't lead to  deadlock as would adding more tables to the 
list possibly lead. 

This is to be done by adding possibility to specify tables to be unlocked to 
UNLOCK TABLES STATEMENT.  So:

UNLOCK TABLES;    - will free all locked tables;

UNLOCK TABLES t1, t2; - will just unlock tables T1,T2 while leaving rest of the 
tables locked.

Also MySQLDUMP may benefit from this feature then performing dump of database
(es) with locking tables. It may free tables after they are dumped without 
waiting for all process to complete. This will give users better concurrency 
by reducing the time then tables can't be updated.