Transaction-scope advisory locks

Hi,

I often find myself wanting advisory locks that are automatically 
released when the transaction ends, so here's a small patch trying to do 
just that.  I don't know much about the lock system so the patch is in 
the state "it looks like this would work".  Any comments on the 
technical details are welcome.  There's obviously a lot of documentation 
and READMEs to change too, but I thought I'd see what people think about 
the idea before going there.

So, thoughts?


Regards,
Marko Tiikkaja