[boost] [smart_ptr] sp_deleter_wrapper

Here's the next patch, this time optimizing sp_deleter_wrapper. It replaces the shared_ptr<void> by shared_count, saving the implicitly stored void*. It also removes _internal_get_deleter and makes enable_shared_from_this use basic_get_deleter to take advantage of the workarounds it provides. OK to commit? BTW: One could also remove _internal_less and use: template<class T, class U> inline bool operator<(shared_ptr<T> const & a, shared_ptr<U> const & b) { return a.get_shared_count() < b.get_shared_count(); } Regards, Daniel