Swap and move boost::pool

Hello,
from a quick look (so I can easily be mistaken) at the implementation of `boost::pool`, it looks like allowing swap and move operations should not cause any major issue. Is that something that you would consider?

Use case: we do not use a global pool (bad for threading), we have a few big objects (usually no more than a handful, or maybe 1-2 per thread) that each own a pool for their internal needs, and we would like to provide swap/move operations on those objects. Wrapping the pool in a unique_ptr is a possibility, but it seems like an unnecessary (small) waste.