[cctbxbb] --enable-boost-threads flag

[Jeffrey Van Voorst]

Ok, let me look into this a bit tomorrow.   The issue is free() which 
gets an invalid address from a shared_ptr for root_data in iotbx_pdb 
when it is time for the whole pdb hierarchy to disappear. My main issue 
is I am not sure how to go about debugging shared_ptrs nor what 
architecture dependent flags or other voodoo (if any) is specified by 
-pthread.

I can do the usual thing of printing out addresses and comparing them by 
eye, but I was hoping that there might be a better and more efficient 
method of debugging shared_ptrs.

--Jeff