[gclist] collector optimization

[Ji-Yong D. Chung]

    Hi

> One thing to watch out for here -- if you are generating
> code at the C level, and you insert assignments to zero
> out dead pointers, and you feed it to a decent C compiler,
> it will turn right around and remove those nulling assignments.      
    
    Thank you for pointing that out.  

    Doing code work only to have a compiler rub them out -- 
that not only would have been an example of highly inefficient coding, 
but also embarassing.  :)
    
    -- More embarassing than making a mistaken claim on 
the execution cost of assembly instruction XCHG, and then
emailing your claim to 10000000000000 people.