shared_ptr_base.h (_Sp_counted_ptr): Make 'final'.

	* include/bits/shared_ptr_base.h (_Sp_counted_ptr): Make 'final'.
	(_Sp_counted_deleter): Make 'final'. Use allocator_traits.
	(_Sp_counted_ptr_inplace): Make 'final'. Use allocator_traits.
	Derive from _Sp_counted_ptr instead of _Sp_counted_deleter to use EBO
	for the allocator.
	(__shared_count, __shared_ptr): Use allocator_traits.
	* include/std/future (__future_base::_Result_alloc): Make 'final'. Use
	allocator traits.
	(__future_base::_Task_state): Make 'final'.
	(__future_base::_Deferred_state): Likewise.
	(__future_base::_Async_state): Likewise.
	* testsuite/20_util/shared_ptr/cons/alloc_min.cc: New.
	* testsuite/20_util/shared_ptr/creation/alloc_min.cc: New.
	* testsuite/20_util/shared_ptr/creation/private.cc: New.
	* testsuite/20_util/shared_ptr/cons/43820_neg.cc: Adjust line numbers.
	* testsuite/30_threads/packaged_task/cons/alloc_min.cc: New.
	* testsuite/30_threads/promise/cons/alloc_min.cc: New.

From-SVN: r181171