[boost] [block_ptr] 20% speed boost

If I try out the latest modifications and I disable the threads then on Linux I have:

make: auto_ptr: 2458626 ns shared_ptr: 2685224 ns block_ptr: 28300624 ns

new: auto_ptr: 2383605 ns shared_ptr: 4992185 ns block_ptr: 7979659 ns

So I just added a specialization of the pool for GCC x86 and now block_ptr<> speeds up by 20%: make: auto_ptr: 2511658 ns shared_ptr: 2695469 ns block_ptr: 22547960 ns new: auto_ptr: 2369312 ns shared_ptr: 4991352 ns block_ptr: 6443925 ns Thanks, -Phil