[GC] Made get_free_*_item() funcs decrement counts.
[GC] Made get_free_*_item() funcs decrement counts.

Now those accessor functions track the counts of free items in the pool.

FROGGS/parrot,youprofit/parrot,FROGGS/parrot,tkob/parrot,youprofit/parrot,gitster/parrot,tewk/parrot-select,gitster/parrot,tewk/parrot-select,tewk/parrot-select,FROGGS/parrot,youprofit/parrot,tewk/parrot-select,gitster/parrot,fernandobrito/parrot,tkob/parrot,fernandobrito/parrot,parrot/parrot,gitster/parrot,tkob/parrot,tewk/parrot-select,FROGGS/parrot,youprofit/parrot,parrot/parrot,fernandobrito/parrot,tkob/parrot,FROGGS/parrot,gitster/parrot,youprofit/parrot,parrot/parrot,tkob/parrot,gagern/parrot,FROGGS/parrot,tkob/parrot,gagern/parrot,parrot/parrot,fernandobrito/parrot,gitster/parrot,FROGGS/parrot,gagern/parrot,parrot/parrot,youprofit/parrot,fernandobrito/parrot,fernandobrito/parrot,tewk/parrot-select,youprofit/parrot,gagern/parrot,gagern/parrot,fernandobrito/parrot,youprofit/parrot,FROGGS/parrot,tkob/parrot,gagern/parrot,tkob/parrot,gagern/parrot,tewk/parrot-select,gitster/parrot