[Bug libstdc++/60448] swap_ranges does not use ADL correctly

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60448

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #6)
> libc++ sfinae constrains std::swap.

Aha!  I suppose we could do that too, but that would be an enhancement (and
have to wait until after the 4.9 release), but apart from that I think we agree
now this is not a bug.