[patch] Make std::deque meet C++11 allocator requirements

[Jonathan Wakely]

This was a tricky one, because std::deque always has a map of nodes
allocated, so needs to re-allocate in its move constructor. That makes
move assignment complicated, as the rvalue object must be left in a
valid state owning memory that can be freed by its (possibly
moved-from) allocator.

The _M_replace_map(_Args&&...) function constructs a new deque from
its arguments, rips the guts out of that new deque and then destroys
it. When the argument to the new deque is an rvalue deque the move
constructor takes care of leaving the rvalue in a valid state with
memory that can be freed by its allocator.

The common case with std::allocator allows move-assignment to be
noexcept, because it only involves swapping a few pointers and calling
clear().

As an extension we support move assignment of std::deque even if the
element types are not assignable, as long as the allocator type
propagates (as we do for std::vector, see PR52591).

Tested x86_64-linux, normal, debug and profile modes.

Committed to trunk.
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