Add support for "fancy" pointers to promise and packaged_task.

Summary:
This patch is very closely related to D4859. Please see http://reviews.llvm.org/D4859 for more information.

This patch adds support for "fancy" pointers and allocators to promise and packaged_task. The changes made to support this are exactly the same as in D4859.



Test Plan: "fancy" pointer tests were added to each constructor affected by the change.

Reviewers: danalbert, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4862

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@220471 91177308-0d34-0410-b5e6-96231b3b80d8