[boost] [shifted_ptr] Allocator added

Hola, I just finalized the design of shifted_ptr by adding a wrapper allocator called sh::pool. This can eventually be used as a second template argument over STL containers. Now shifted_ptr is bulletproof.... Once again I think there is some sort of stack overflow on GCC for Windows when Boost.Test macros are used so please us shifted_ptr_test2.cpp in that case. I am not sure also if Stephen Cleary has any intent extending Boost.Pool to handle arbitraty sized chunks, that would basically be the final step for having even faster allocations. I uploaded it on Vault and the Sandbox. Thank you, -Phil