[cctbxbb] Boost Python 1.56

Hi, I have improvements to the smtbx on their way to be committed which require Boost version 1.56. This is related to Boost.Threads, whose support I re-activated a few months ago on Nick’s request. I need the function boost::thread::physical_concurrency which returns the number of physical cores on the machine, as opposed to virtual cores when hyperthreading is enabled (which it is by default on any Intel machine). That function is not available in Boost 1.55 which is the version currently used in the nightly tests: it appeared in 1.56. So, would it be possible to move to Boost 1.56? Otherwise, I will need to backport that function. Not too difficult but not thrilling. Best wishes, Luc