[c++0x] shared_ptr comparisons

[Jonathan Wakely]

Update std::shared_ptr with the changes from n2637, such that
operator< compares the stored pointers not the addresses of the
control blocks.

I also took Chris's suggestion to use deleted functions in
_Sp_counted_ptr and I fixed the std::swap overloads for
shared/weak_ptr (which are needed in addition to the
__shared/__weak_ptr overloads in case users take the function's
address.)

Tested x86_64-unknown-linux-gnu. OK for mainline? I know we're late in
stage 3 but this only touches experimental C++0x stuff, and n2637
makes significant changes, so IMHO it would be good for both GCC and
C++0x if 4.4 implements the new ordering semantics.

N.B. the 20.8.13... section numbers are already wrong, because CD1 has
different numbering to n2798 ... ship happens.

Jonathan

        * include/bits/shared_ptr.h: Update comparisons to match WP.
        (_Sp_counted_ptr): Make copy and assignment members deleted.
        (_Sp_counted_deleter): Remove private copy and assignment members.
        (__shared_count::_M_less,__weak_count::_M_less,operator<): Replace
        friend operator< with overloaded _M_less member functions to allow
        comparison with either shared_count or weak_count.
        (__shared_ptr::_M_less,__weak_ptr::_M_less): Replace with...
        (__shared_ptr::owner_before,__weak_ptr::owner_before): New overloads
        for ownership-based ordering.
        (operator<(__shared_ptr,__shared_ptr)): Compare stored pointers,
        make non-friend.
        (operator==(__shared_ptr,__shared_ptr)): Make non-friend.
        (operator!=(__shared_ptr,__shared_ptr)): Likewise.
        (less<__shared_ptr<>>,less<shared_ptr<>>,_Sp_less): Explicitly call
        pointer specialization.
        (__weak_ptr::operator<,weak_ptr::operator<=,weak_ptr::operator>,
        weak_ptr::operator>=): Remove operator< and delete all comparisons.
        (_Sp_owner_less,owner_less): Predicate for ownership-based ordering.
        (operator<(shared_ptr,shared_ptr): Overload for derived shared_ptr.
        (operator==(shared_ptr,shared_ptr): Likewise.
        (operator!=(shared_ptr,shared_ptr): Likewise.
        (swap(shared_ptr,shared_ptr)): Fix parameter types.
        (swap(weak_ptr,weak_ptr)): Add missing overload.
        * testsuite/20_util/owner_less/cmp.cc: New.
        * testsuite/20_util/shared_ptr/comparison/cmp.cc: Test other ops.
        * testsuite/20_util/shared_ptr/comparison/less.cc: New.
        * testsuite/20_util/shared_ptr/observers/owner_before.cc: New.
        * testsuite/20_util/weak_ptr/observers/owner_before.cc: New.
        * testsuite/20_util/weak_ptr/comparison/cmp_neg.cc: New.
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