Update boost

This set of patches should update libmesh's internal boost distribution to version 1.55.0.

This was pretty straight-forward except for some slight differences to the pool allocator which are discussed in more detail here: http://stackoverflow.com/questions/17000542/boost-pool-can-i-wean-it-from-boost-system

@benkirk, are we actually using the pool allocator in the library at all?  If you have test code that uses Boost.Pool, would you mind trying it out on this new Boost?  Thanks!