[gclist] gc concerns

[Charles Fiterman]

I basically agree with Hans but wish to add another reason.

We have pseudo incremental mode. The user needs to write a gcIdle()
function that returns 1 if collection can continue and 0 if collection must
be halted for user responce. In pseudo incremental mode collection proceeds
either to finish or to an event that would make the user aware of delay. A
good example would be one second after a mouse click or key press without
mutator action. 

So if gcIdle() halts a collection the work is simply thrown away. Our
results with pseudo incremental collection make us think incremental
collection isn't really important.