Implement registry key unloading

[Steven Edwards]

> ChangeLog:
> * Implement registry key unloading

Speaking of the registry if you guys are interested in implementing a 
faster binary format for the registry take a look at what we have done 
in ReactOS. Eric Kohl has offered to license his work as LGPL if you 
guys want to try to move to the same format we use. It should be much 
faster then the existing system currently in WINE. Now that we have a 
GUI regedit for WINE and ReactOS once write support is implemented then 
it might be a good idea to implement this.

Thanks
Steven