Various memory fix/features

- aligned_malloc/free/realloc now have an overload that take
an arbitrary function object to perform the basic task.
- aligned_reuse is now implementable without aligned_realloc.
- force inlining were removed where unecessary.
- added doc on the malloc override mecanism
fix includes of aligned_free/aligned_malloc/aligned_realloc. Also define NO_BUILTINS if a custom function is defined.
make it explicit which function we're calling in memory builtins contexts, mark potential problem in posix realloc
Fix allocator code factorization
_aligned_malloc instead of _aligned_alloc in reallocate
Missing include in aligned_reuse
fix bad reallocate unit test
fix various problems with aligned allocation primitives. MSVC built-ins now store the alignment before the pointer, because for now we allow aligned_realloc to change the alignment. Stashed implementation now also stores the allocated size on top of the used size, which is however only needed for allocators. Also replaced the hardcoded 32 by the macro BOOST_SIMD_REALLOC_SHRINK_THRESHOLD
add missing aligned_reuse optimization, doesn't need the memmove of aligned_realloc
add test before calling memmove, implementation doesn't test whether destination and source are the same.
Fix alignment misnaming
Fixed doc on custom alloc/dealloc behavior
Fix memmov error in aligned_realloc
Fix warning about unitialized field in header_block
divceil refurbishing and correcting
fix includes in divceil test + don't hardcode int64_t which is obviously not supported everywhere
divfloor refurbishing and correcting and too much includes in divceil.hpp
correcting hard coded int64_t in floor.cpp
Fix hanging on some benchmarks

Boost.Random behaves badly when asked to roll a number between
Valmin and Valmax as a real. As the benchmarks take little
care about the actual boudnaries, we opt to use Valmin/2 and
Valmax/2 for now.
restoring ceil and floor to their previous code: use round2even for all floating-point types. If SSE optimization there must be, it should be in elsewhere.